Johann Harel
email: johann.harel@chu-bordeaux.fr

Romain Fossaert
email: romain.fossaert@chu-bordeaux.fr

Alain Bérard

Aurélie Lafargue
email: aurelie.lafargue@chu-bordeaux.fr

Marie Danet-Lamasou

Philippe Poisson
email: phpoisson@wanadoo.fr

Véronique Dupuis
email: veronique.dupuis@chu-bordeaux.fr

Isabelle Bourdel-Marchasson
email: isabelle.bourdel-marchasson@chu-bordeaux.fr

Isabelle Bourdel

Masticatory coefficient and physical functioning in older frail patients admitted for a Comprehensive Gerontological Assessment

Keywords: multimorbidity, masticatory capacities, physical performance, malnutrition CRediT roles: Conceptualization: JH, RF,AB, IBM, Data curation: HR, AL, Formal analysis: AL, PP, IBM, Investigation: AB, MDL, VD, frailty, oral health, poly-morbidity, comprehensive gerontological assessment, physical performance, malnutrition

Comprehensive Gerontological Assessment in multi-morbid and frail older patients can include intraoral exam

In multi-morbid patients impaired mastication capacities are associated with malnutrition In frail un multi-morbid patients lower limb performance is lower with lower masticatory capacities independently from nutritional status

Introduction

The prevention of both decompensation due to chronic disease and functional dependence is an important goal in the care of older people. The comprehensive gerontological assessment (CGA) is based on systematic screening and scoring of four domains: mental health, functionality, medical status and social status(Kenneth [START_REF] Rockwood | Comprehensive geriatric assessment[END_REF][START_REF] Valencia | Assessment procedures including comprehensive geriatric assessment[END_REF]. The resulting care plan has been shown to prevent a worsening of health, particularly in frail patients. In older people, frailty refers to a multifactorial impairment of health that predicts adverse living events, such as loss of independence, hospitalization, adverse drug reactions, decompensation related to chronic disease, admission to a nursing home, or death [START_REF] Fried | Frailty in older adults: evidence for a phenotype[END_REF][START_REF] Rockwood | A brief clinical instrument to classify frailty in elderly people[END_REF]. Effective preventive strategies in older people may thus rely on the identification of those who are frail. Poor oral health in hospitalized older patients was found strongly associated with poor functional status or malnutrition [START_REF] Poisson | Relationships between oral health, dysphagia and undernutrition in hospitalised elderly patients[END_REF]. Thus, frailty may be linked to oral health as a possible determinant of multifactorial development of this syndrome. Indeed, several studies have reported cross-sectional relationships between components of oral health and frailty. Loss of teeth, an unmet need for a fixed prosthesis or removable denture, self-reported poor oral health, and pain or impaired mastication are among the factors associated with an increased prevalence of frailty [START_REF] Castrejón-Pérez | Oral health conditions and frailty in Mexican community-dwelling elderly: a cross sectional analysis[END_REF][START_REF] Kamdem | Relationship between oral health and Fried's frailty criteria in community-dwelling older persons[END_REF][START_REF] Semba | Denture use, malnutrition, frailty, and mortality among older women living in the community[END_REF][START_REF] Tsai | Association of dental prosthetic condition with food consumption and the risk of malnutrition and follow-up 4-year mortality risk in elderly Taiwanese[END_REF][START_REF] Woo | Chewing difficulty should be included as a geriatric syndrome[END_REF]. Finally, masticatory dysfunction, number of missing teeth, and dry mouth were identified among the factors that increase the rate of progression of the prefrail or robust older people to a frail status [START_REF] Hakeem | Association between oral health and frailty: A systematic review of longitudinal studies[END_REF][START_REF] Horibe | Relationship between masticatory function and frailty in community-dwelling Japanese elderly[END_REF]. Oral health behavior also varies according to frailty status, as older individuals with several health complaints may neglect oral hygiene [START_REF] Niesten | The impact of frailty on oral care behavior of older people: a qualitative study[END_REF].

CGA is essentially multidisciplinary; evaluation is performed by a basic team consisting of a medical practitioner, a nurse, and a social worker; depending on the patient profile, it may be supplemented by a psychologist, a physiotherapist, an occupational therapist, and/or a pharmacist.

Given the importance of oral health in the general health status of older subjects, an intra-oral health examination carried out by a dentist should be performed and care should be proposed if indicated.

The oral exam should be conducted as part of the medical section, along with a nutritional assessment [START_REF] Valencia | Assessment procedures including comprehensive geriatric assessment[END_REF]. In the older adult poor oral health, in particular a loss of teeth is associated with a low-quality diet [START_REF] Gaewkhiew | Functional dentition, dietary intake and nutritional status in Thai older adults[END_REF][START_REF] Kiesswetter | Functional determinants of dietary intake in community-dwelling older adults: a DEDIPAC (DEterminants of DIet and Physical ACtivity) systematic literature review[END_REF][START_REF] Mendonça | Prevalence and determinants of low protein intake in very old adults: insights from the Newcastle 85+ Study[END_REF]. Impaired mastication may be due to a loss of teeth or to a non-functional removable prosthesis [START_REF] Iwasaki | The association between dentition status and sarcopenia in Japanese adults aged ≥75 years[END_REF] and contributes to sarcopenia. An intraoral examination may have added value beyond that of a component of the nutritional assessment.

The functional domain assessment includes scoring of daily living activities and assessments of physical performance and fall risk. Two tools are available for this purpose: the short physical performance battery (SPPB) [START_REF] Guralnik | A Short physical performance battery assessing lower extremity function: association with self-reported disability and prediction of mortality and nursing home admission[END_REF] and the timed up and go test (TUG) [START_REF] Podsiadlo | The Timed "Up & Go": A test of basic functional mobility for frail elderly persons[END_REF]. These two tests explore balance, gait speed and rising from a chair.

We hypothesized that in the older frail or dependent subjects, functional impairment assessed using the SPPB or TUG would be more important in the subgroup with missing teeth, particularly individuals with a non-functional removable prosthesis or without a needed prosthesis. The objective of the present study is to analyze relationships between functional impairment and an index of missing teeth recorded as geriatric masticatory coefficient taking into account nutritional status.

Materials and Methods

This cross-sectional study included consecutive patients older than 70 years who were admitted to a single geriatric day hospital for CGA as part of routine care during a 2-year period. Based on the usual activity of the unit the duration of the inclusion period was selected to include at least 10 subjects per descriptive variables. Patients received written information about the use of their anonymized health data for clinical research purposes and were given the option of refusal. The study was approved by the Ethical Committee of the CHU (university hospital center) of Bordeaux (GP-CE2020-43).

Patients who had undergone an intra-oral health examination performed by a dentist during the CGA were included in the study. Patients unable to perform the TUG or SPPB were excluded. In case of two or more visits to the day hospital, only the first was considered.

Comprehensive gerontological assessment (CGA)

Co-variables of this study included age, gender, living place (personal home or care home), education (none or no certificate, primary school certificate, secondary school certificate, bachelor and over). Mental health was assessed for depression and cognitive troubles by screening with the 15-Geriatric depression scale (GDS) [START_REF] Yesavage | 9/Geriatric Depression Scale (GDS)[END_REF] and the Gréco French version of mini mental status examination (MMSe), respectively [START_REF] Folstein | Mini-mental state[END_REF][START_REF] Kakafat | Standardisation et étalonnage français du Mini Mental State (Mms) Version Gréco[END_REF]. A GDS score > 4/15 was considered to indicate depression, and an MMSe score < 23/30 was taken to indicate cognitive troubles. The functional domain included TUG or SPPB assessment (see 2.3), basic activities of daily living (ADL) [START_REF] Katz | Assessing self-maintenance: activities of daily living, mobility, and instrumental activities of daily living[END_REF] and instrumental activities of daily living (IADL) [START_REF] Lawton | Assessment of Older People: Self-Maintaining and Instrumental Activities of Daily Living[END_REF]). An ADL score > 1/12 and an IADL score < 8/8 indicated dependence. The medical evaluation included chronic pathologies listing, full treatment list and a nutritional assessment. The latter consisted of a body mass index (BMI, weight (kg)/height (m)², mini nutritional assessment (MNA©) [START_REF] Kaiser | Validation of the Mini Nutritional Assessment short-form (MNA®-SF): A practical tool for identification of nutritional status[END_REF]scoring and dental examination by a dentist (see below). MNA© allows to identify malnutrition (MNA 0-7/14) and at risk for malnutrition . The version of the MNA based on calf circumference (CC) (<31 cm vs. ≥31 cm) instead of BMI was used because CC serves as a surrogate of muscle mass [START_REF] Cruz-Jentoft | Sarcopenia: revised European consensus on definition and diagnosis[END_REF]. Among routine blood sample analyses we selected hemoglobin (g/100 mL), C-reactive protein (mg/L), serum albumin (g/L), and vitamin D (ng/mL) levels. Glomerular filtration rate (eGFR) was estimated using the CKD-Epidemiology Collaboration equation (CKD-EPI) [START_REF] Levey | A new equation to estimate glomerular filtration rate[END_REF] which is based on serum levels of creatinine. Patients were categorized according to the Rockwood clinical frailty scale(K. [START_REF] Rockwood | A global clinical measure of fitness and frailty in elderly people[END_REF].

Geriatric masticatory coefficient (GMC)

In routine care, chewing performance is not measured in these older and frail adults; masticatory teeth capacity is assessed. Mastication involves both posterior occluding pairs of teeth (POPs) and anterior grasping teeth.

The masticatory coefficient (masticatory percentage) [START_REF] Dion | Correction of nutrition test errors for more accurate quantification of the link between dental health and malnutrition[END_REF] is determined by assigning points as follows to each functional tooth according to its role in mastication as long as the opposite tooth is also functional: 5 points for each molar except the third maxillary molar (2 points) and the third mandibular molar (3 points), 3 points for each premolar, 4 points for each canine tooth, and 1 point for each incisor except the central maxillary incisor (2 points). The maximal masticatory coefficient is 100. A modified index, the geriatric masticatory coefficient (GMC), was used because it takes into account all of the person's remaining teeth, not only those belonging to a functional pair [START_REF] Berard | Removable prosthesis improves body mass index in elderly people[END_REF] . Because teeth with missing opposite teeth have a non-zero role during mastication, GMC may better reflect the remaining masticatory capacity. With this approach, individuals with several remaining teeth were not assessed as edentulous. Determining the remaining masticatory capacity is an important point for treatment decisions, such as extraction of teeth or placement of dentures.

In patients wearing a prosthesis, a corrected GMC was similarly determined during clinical observation. Prostheses, fixed or movable, have the value of the teeth they replace, provided they allow a normal meshing. Thus, the variable "corrected GMC" represented the best GMC for each patient, with or without a prosthesis. Finally, the number of POPs (POP, range 0-8) without a prosthesis was also recorded. Pairs of opposite teeth are taken into account providing they allow a correct meshing.

Functional performance

Motor performance was assessed using either the SPPB [START_REF] Guralnik | A Short physical performance battery assessing lower extremity function: association with self-reported disability and prediction of mortality and nursing home admission[END_REF] or the TUG test [START_REF] Podsiadlo | The Timed "Up & Go": A test of basic functional mobility for frail elderly persons[END_REF] depending on the medical practitioner's preference. Both evaluate gait speed, standing balance, and rising from a chair. The SPPB consists of three 4-point scores: 1, standing balance: participants attempt to maintain side-by-side, semi-tandem, and tandem positions for 10 s; 2, a 4 m walk at normal pace timed from a standing start; and 3, time needed to rise from a chair as quickly as possible five times. Overall, the maximal SPPB score is 12 (4 points per test). The TUG test evaluates the same abilities but in a single test that focuses on the risk of falling.

The patient is instructed to rise from a chair (with arms), walk 3 m, turn and return to the chair, and then sit down again. The performance is timed. Cognitive troubles, mainly attention troubles increases time spend in the task. TUG explores the risk of falling.

Analyses

The inclusion period duration was selected to obtain a sample with at least 10 patients for each described variables based on the usual activity of the unit. Quantitative variables are expressed as the mean and standard deviation (SD), ordinal variables (scores) are shown as median (IQR, interquartile range) and qualitative variables are given as numbers and percentages. SPPB is an ordinal variable and is also expressed as mean (SD). Because the link between dental status and malnutrition is well established, the characteristics of the patients are presented according to MNA categories and the different categories are compared using a chi-square test for qualitative variables and a one-way ANOVA for quantitative variables. Correlations between GMC, corrected GMC, or POPs and the SPPB or TUG test were determined using Spearman coefficient tests. Because SPPB is an ordinal variable and TUG is not normally distributed in frail or dependent patients, partial correlation tests were performed to analyze the relationships between corrected GMC, GMC, and POPs and SPPB or TUG, controlling for age, sex, and MNA category to identify the role of malnutrition in those relationships. The software SPSS 23 (IBM®) was used for these analyses.

Results

During the study period, 302 patients underwent a CGA that included an intra-oral examination.

After the exclusion of 39 patients due to a missing physical performance assessment in their CGAs and 7 patients each of whom underwent two CGAs, the study sample included 256 patients.

The characteristics of the study population are presented in Table 1. The SPPB test was performed in 91 patients and the TUG test was performed in 211. Serious chronic diseases had a high prevalence and included heart failure in 76 (29.7%), respiratory diseases in 32 (12.5%), major cognitive troubles in 110 (44.4%), history of cancer in 59 (23.0%), stroke in 43 (16.8%), diabetes mellitus in 82 (32.0%), and hypertension in 185 (72.5%) patients. The number of medications taken daily by these patients was also high: 6.9 (SD 3.5), with five or more different medications taken by 191 (74.9%) patients. Chronic inflammation was of low-medium intensity as reflected by a mean Creactive protein level of 7.7 (15.3) mg/L. Vitamin D levels were <10 ng/mL in 48 (22.1%) patients; 31 (13.0%) patients had severe renal insufficiency (CKD-EPI<30 mL/min/1.73 m2).

Functional ADL or IADL dependence was present but at low levels. According to the frailty scale most of the subjects were classified in the categories "mildly frail" (79 (32.1%)) or "moderately frail" (77 (31.3%)). The others were either in the category "managing well" (25 (9.8%)) or at the opposite in the other "severely frail" (36(14.6%)).

Malnutrition and risk of malnutrition were frequent, identified in 75 (30.5%) and 126 (51.2%) patients, respectively. Patients living in a nursing home, with a higher 15-GDS, lower MMSe, major cognitive troubles, or a higher level of dependence were more likely to be malnourished or at risk of malnutrition.

The physical performance of the population was poor, evidenced by an SPPB score of <8/12 in 59 (64.8%) patients and a TUG score ≥ 20 s in 102 (46.4%) patients. The SPPB score was lower in malnourished patients and in patients at risk for malnutrition than in normo-nourished patients.

The dental examinations showed important impairments, based on a low GMC and the low number of POPs: 53.7/100 (SD 30.6) and 3.1/8 (SD 3.0), respectively. One hundred and five patients had a dental prosthesis. After correction for patients with a prosthesis, the corrected GMC was 75.4 (SD 19.8). While the corrected GMC was related to the MNA category, this was not the case for either the GMC or the number of POPs.

After controlling for age, gender and MNA category, an association between the corrected GMC and both the TUG time (-0.198, p = 0.005) and the SPPB score (0.282, p = 0.009) was determined (Table 2). Both the GMC and POPs were associated with the SPPB score (GMC: 0.269, p = 0.013; POPs: 0.319, p = 0.004) but not with the TUG time (Table2).

Discussion

We found a cross-sectional association between nutritional status, corrected GMC, and physical performance in the mildly to severely frail older adult with complex health problems. The association between the corrected GMC and physical performance was independent of nutritional status.

Masticatory capacity was evaluated using two different approaches, pairs of opposing teeth and number of teeth, weighted according to their alleged role in mastication. The adjusted partial correlations showed relationships between both indexes and the SPPB score.

An association between diminished masticatory capacity and malnutrition in the older people has previously been reported [START_REF] Toniazzo | Relationship of nutritional status and oral health in elderly: Systematic review with meta-analysis[END_REF]. Because malnutrition is associated with low muscle strength [START_REF] Veronese | Effect of nutritional supplementations on physical performance and muscle strength parameters in older people: A systematic review and meta-analysis[END_REF] lower muscle performance is expected in patients with impaired corrected masticatory coefficient. However, malnutrition does not fully explain the link between a lower corrected GMC and lower physical functioning of the limbs. Physical performance relies not only on strength but also on balance, proprioceptive functions, and several cognitive processes, such as attention. Teeth clenching may reinforce balance through a facilitation of the pretibial reflex that is related to applied strength [START_REF] Takada | Modulation of H reflex of pretibial muscles and reciprocal Ia inhibition of soleus muscle during voluntary teeth clenching in humans[END_REF]. Postural balance may be improved during chewing [START_REF] Alghadir | Effect of chewing on postural stability during quiet standing in healthy young males[END_REF]. A loss of teeth may directly impact physical performance, particularly balance. Pain, inflammatory syndromes, and dyspnea also diminish physical performance. In a previous study, these relationships were considered in a fully adjusted model, in which the presence of 19 or less teeth not corrected with a prosthesis was found to increase the risk of falling [START_REF] Yamamoto | Dental status and incident falls among older Japanese: a prospective cohort study[END_REF].

The most common characteristic of our frail study population was the high prevalence of severe comorbidity, including cardiovascular diseases, diabetes, COPD and asthma, cognitive troubles, or a history of stroke. The physical performance of patients with severe comorbidities is frequently impaired. The comorbidities are possibly secondary to the loss of teeth. In three community studies, each missing tooth increased cardiovascular risk and mortality [START_REF] Holmlund | Number of teeth as a predictor of cardiovascular mortality in a cohort of 7,674 subjects followed for 12 Years[END_REF][START_REF] Joshy | Is poor oral health a risk marker for incident cardiovascular disease hospitalisation and all-cause mortality? Findings from 172 630 participants from the prospective 45 and Up Study[END_REF][START_REF] Lee | Tooth Loss Predicts Myocardial Infarction, Heart Failure, Stroke, and Death[END_REF]. In a large cross-sectional study, severe tooth loss and a history of stroke were independently associated with inflammation [START_REF] You | Tooth loss, systemic inflammation, and prevalent stroke among participants in the reasons for geographic and racial difference in stroke (REGARDS) study[END_REF]. Missing teeth may predict a higher risk for cognitive impairment [START_REF] Zhang | Poor oral health conditions and cognitive decline: Studies in humans and rats[END_REF]. In nursing home residents, patients with missing POPs without prostheses have an increased 1-year mortality, independent of nutritional status [START_REF] Dewake | Posterior occluding pairs of teeth or dentures and 1-year mortality in nursing home residents in Japan[END_REF]. However, the causal link between missing teeth and the above-listed pathologies is probably multifactorial and bi-directional [START_REF] Felton | Complete edentulism and comorbid diseases: an update[END_REF]. Furthermore, some risk factors for tooth loss are shared by systemic diseases. Low-medium grade inflammation due to periodontitis can cause both systemic inflammation (and cardiovascular diseases) and a loss of teeth.

Chronic oral inflammation may induce dental loss and increase the risk for cardiovascular disease, malnutrition, and muscle functional impairment. Finally, the behavioral changes that occur with severe disease are likely to impair both self-care and access to professional care, thus worsening oral health.

In our study population, the association between masticatory capacity and physical performance was better described by the corrected GMC than the GMC, given that prosthetic adaptation protects against a physical decline. As demonstrated by a previous study showing an improvement in cardiovascular risk with better oral care [START_REF] Park | Improved oral hygiene care attenuates the cardiovascular risk of oral health disease: a population-based study from Korea[END_REF] dental care within the scope of the CGA holds promise in the management of complex health problems in the older adults.

The limitations of our study should be noted. First, it was a cross-sectional study and causality could not be determined. Second, masticatory capacity, not function, was assessed. Tests for chewing ability, such as using color-indicator gums and measures of masseter or hand grip strength, are not done in routine care. However, an association between impaired chewing ability and weaker occlusal forces with sarcopenia was determined in a previous study of the community-dwelling elders [START_REF] Murakami | Relationship between chewing ability and sarcopenia in Japanese community-dwelling older adults[END_REF]. Therefore, low muscle strength may also affect the muscles involved in mastication (masseter, tongue, cheeks). In routine clinical practice, a "static" assessment of masticatory capacity in frail, older patients can be easily and reliably performed. Third, several subject characteristics potentially associated with the study variables were not recorded and therefore not analyzed: smoking and alcohol use and usual physical activity. Finally, this study did not permit to clarify the role of multi-morbidity in the relationship between masticatory capacities and physical performance. Among the strengths of our study were the large sample population and the inclusion of frail older individuals engaged in preventive action to decrease the burden of multimorbidity. Our results show that oral care has a role to play in preventing functional decline in the frail elderly. Finally the magnitude of the correlation is not outstanding.

Conclusions

In older mildly to severely frail and multi-morbid patients, the physical performance will be limited in those with a loss of teeth. In addition, malnutrition is not the only link between chronic diseases, oral health and posture. An impaired posture may be due to missing teeth. A longitudinal study should explore the effects of dental care on physical performance in multi-morbid older patients.

Table 1 .

 1 Characteristics of the patients according to Mini-Nutritional Assessment (MNA) category.

		All subjects	MNA 0-7	MNA 8-11	MNA 12-14	P value*
	Characteristics	N = 256	Malnutrition	At risk of	Normal	Comparison
			N = 75	malnutrition	N = 45	according to
				N = 126		MNA classes
	Age	83.8 (6.2)	83.3 (5.4)	84.6 (5.5)	84.0 (4.3)	<0.001
	Gender (F/M)	148/108	47/28	79/47	18/27	0.020
	Educational level					0.389
	-no certificate	63 (25.2)	20 (27.8)	34 (27.6)	8 (17.8)
	-primary school
	certificate	87 (34.8)	27 (37.5)	46 (37.4)	11 (24.4)
	-secondary school
	certificate	43 (17.2)	11 (15.3)	19 (15.4)	10 (22.2)
	-bachelor and over	57 (22.8)	14 (19.4)	26 (19.5)	16 (35.5)
	Living place	20 (7.8)	13 (17.3)	4 (3.2)	0 (0)	<0.001
	(nursing home)
	BMI (kg / m²)	26.5 (5.3)	24.1 (5.0)	26.4 (3.9)	28.2 (5.8)	<0.001
	Calf circumference	33.0 (3.9)	31.6 (3.5)	33.6 (3.6)	36.1 (3.7)	<0.001
	(cm)
	GMC (0-100)	53.7 (30.6)	43.6 (4.3)	58.9 (31.0)	71.3 (9.3)	0.096
	Corrected GMC (0 -	75.4 (19.8)	75.9 (20.9)	77.6 (15.9)	77.3 9.4)	<0.001
	100)
	POPs (n)	3.1 (3.0)	2.6 (3.6)	3.6 (3.2)	4.3 (2.2)	0.056
	TUG (s)	22.0 (14.6)	22.0 (11.4)	25.3 (11.5)	18.8 (7.3)	0.303
	SPPB (0-12)	6 (7)	4 (4)	4 (6)	10 (3)	<0.001
	MMSe (0-30	23 (9)	23 (7)	22 (9)	29 (3)	<0.001
	15-GDS (0-15)	6 (6)	8 (6)	7 (6)	4 (3)	<0.001
	ADL (0-12)	1 (4)	3 (6)	2 (5)	0 (0)	0.005
	IADL (0-8)	4 (6)	2 (3)	2 (5)	7 (3)	<0.001
	Diabetes (yes)	82 (32.0)	26 (34.7)	36 (28.6)	18 (40.0)	0.333
	Stroke history	43 (16.8)	15 (20.0)	15 (11.9)	11 (24.4)	0.099
	Cognitive troubles	110 (44.4)	42 (59.2)	60 (48.8)	4 (9.1)	<0.001
	Hypertension	185 (72.5)	57 (76.0)	84 (67.2)	38 (84.4)	0.065
	History of cancer	59 (23.0)	16 (21.3)	27 (21.4)	14 (31.1)	0.377
	Heart failure	76 (29.7)	18 (24.0)	38 (30.2)	17 (37.8)	0.274
	COPD-asthma	32 (12.5)	8 (10.7)	14 (11.1)	9 (20.0)	0.253
	Number of	6.9 (3.48)	6.7 (3.2)	6.7 (3.5)	8.5 (3.8)	0.479
	medication
	eGFR (CKD-EPI,	65.0 (19.9)	66.4 (15.1)	65.2 (14.0)	62.4 (28.9)	<0.001
	mL/min / 1.73m²)
	C-reactive protein	7.7 (15.7)	23.4 (51.2)	9.3 (14.0)	3.9 (4.1)	0.553
	(mg /L)
	Serum albumin	37.7 (4.0)	36.8 (4.5)	36.9 (3.1)	38.3 (4.0)	0.123
	(g /L)
	Hemoglobin (g / 100	13.0 (1.5)	12.6 (1.6)	13.1 (1.4)	12.9 (1.2)	0.231
	mL)
	Vitamin D	22.3 (13.0)	27.2 (14.1)	28.2 (19.3)	19.5 (9.7)	0.162
	(ng / mL)

Variables are presented as Mean (SD), Median (Interquartile range) or N (%). POPs: posterior occluding pairs of teeth; GMC: geriatric masticatory coefficient; TUG: timed up and go test; SPPB: short physical performance battery; MMSe : mini mental state examination; GDS geriatric depression scale; ADL basic activities of daily iiving; IADL: instrumental activities of daily living; eGFR: estimated glomerular filtration rate;. *Quantitative variables were compared using oneway ANOVA and qualitative variables using Chi2 test.

Table 2 .

 2 Correlations between physical performance assessment and masticatory capacity assessment based on the number of teeth

	TUG


Philémon Marcel-Millet
email: philemon.marcel-millet@edu.univ-fcomte.fr

Alain Groslambert
email: alain.groslambert@univ-fcomte.fr

Philippe Gimenez
email: philippe.gimenez@univ-fcomte.fr

Sidney Grosprêtre
email: sidney.grospretre@univ-fcomte.fr

Gilles Ravier
email: gilles.ravier@univ-fcomte.fr

Philémon Marcel

Psychophysiological responses of firefighters to day and night rescue interventions

Keywords: firefighting activity, autonomic nervous system, heart rate variability

This study aimed 1) to assess the psychophysiological responses throughout a rescue intervention performed during the day and at night and 2) to determine if a vibrating alarm influences these psychophysiological responses at night. Sixteen male firefighters completed a simulated intervention under three different conditions: 1) during the day with a sound alarm signal (DaySA), 2) during the night with a sound alarm signal (NightSA), 3) during the night with a vibrating alarm signal (NightVA). Cardiovascular and psychological stress were recorded throughout the interventions.

During the alarm signal, HR reactivity was greater in NightSA than in DaySA (p<0.01). Parasympathetic reactivation and self-confidence were significantly lower in NightSA than in DaySA (p<0.05). HR reactivity was decreased in NightVA in comparison to NightSA (p<0.05).

Overall, the rescue intervention had a greater impact on the psychophysiological variables during the night than during the day, and the type of alarm had a minor effect.

Introduction

Firefighting is a very demanding occupational activity that leads to a with high level of psychophysiological stress during rescue interventions [START_REF] Williams-Bell | Physiological demands of the firefighter candidate physical ability test[END_REF][START_REF] Horn | Physiological recovery from firefighting activities in rehabilitation and beyond[END_REF][START_REF] Horn | Firefighter and fire instructor's physiological responses and safety in various training fire environments[END_REF][START_REF] Smith | Cardiovascular strain of firefighting and the risk of sudden cardiac events[END_REF][START_REF] Windisch | Physiological Responses to Firefighting in Extreme Temperatures Do Not Compare to Firefighting in Temperate Conditions[END_REF]. It is important for firefighters to be physically fit in order to enhance their firefighting performance, which can be quantified by the time required to carry out their duties [START_REF] Williams-Bell | Physiological demands of the firefighter candidate physical ability test[END_REF], as well as by the associated physiological responses [START_REF] Windisch | Physiological Responses to Firefighting in Extreme Temperatures Do Not Compare to Firefighting in Temperate Conditions[END_REF]. In France, firefighters work a 24-hour shift, so they have to maintain a high level of performance regardless of the time of day or night. However, to date, firefighters' performance and physiological stress in response to interventions have only been studied during the day [START_REF] Williams-Bell | Physiological demands of the firefighter candidate physical ability test[END_REF][START_REF] Horn | Physiological recovery from firefighting activities in rehabilitation and beyond[END_REF][START_REF] Horn | Firefighter and fire instructor's physiological responses and safety in various training fire environments[END_REF][START_REF] Windisch | Physiological Responses to Firefighting in Extreme Temperatures Do Not Compare to Firefighting in Temperate Conditions[END_REF]) except for the acute response to the alarm signal, which has been compared between day and night conditions [START_REF] Hall | The acute physiological stress response to an emergency alarm and mobilization during the day and at night[END_REF]. The authors showed that the increase in heart rate (HR) was similar during the day and night, whereas the increase in cortisol was higher at night than during the day. Several studies conducted with healthy subjects have shown that physical performance is better late in the afternoon than in the early morning [START_REF] Baxter | Influence of time of day on all-out swimming[END_REF][START_REF] Thun | Sleep, circadian rhythms, and athletic performance[END_REF].

However, these results appear to be equivocal, and other studies revealed no effect of circadian rhythm on physical performance [START_REF] Reilly | Investigation of circadian rhythms in metabolic responses to exercise[END_REF][START_REF] Deschenes | Chronobiological effects on exercise performance and selected physiological responses[END_REF]. Moreover, at rest, several physiological functions, such as rectal temperature, HR, plasma lactates, blood pressure (BP) or and cortisol levels, follow a circadian rhythmicity [START_REF] Reilly | Investigation of circadian rhythms in metabolic responses to exercise[END_REF][START_REF] Deschenes | Chronobiological effects on exercise performance and selected physiological responses[END_REF], which can also be found during or after exercise [START_REF] Harma | Circadian variation of physiological functions in physically average and very fit dayworkers[END_REF]. These results are controversial since other studies did not show any circadian variations in HR responses at with exercise [START_REF] Reilly | Investigation of circadian rhythms in metabolic responses to exercise[END_REF][START_REF] Deschenes | Chronobiological effects on exercise performance and selected physiological responses[END_REF]. Consequently, the general picture of the circadian modulations of performance and physiological variables is unclear. It seems that this variation should be highly dependent upon the type of exercise and the characteristics of the participants.

Moreover, beyond the circadian variations, the state (awake / asleep) in which the firefighter is in, at the time of the intervention, can influence his or her psychophysiological responses. Indeed, HRV and HR seem to be largely under a sleep-wake-dependent process [START_REF] Viola | Sleep processes exert a predominant influence on the 24-h profile of heart rate variability[END_REF]. Therefore, it would be important for the safety and security of firefighters to measure if the performance of firefighters is modulated by the moment of the intervention (daytime vs night-time).

Moreover, the psychophysiological stress resulting from firefighting activities depends on the interaction of three different phases during an intervention. The first phase, the alarm mobilisation phase, corresponds to the alarm signal followed by the moment when firefighters change into their protective clothing before leaving the fire station. This phase leads to physiological stress with an increase of HR from 20 to 66 beats⋅min -1 in a short period of time [START_REF] Kuorinka | Firefighters' reaction to alarm, an ECG and heart rate study[END_REF][START_REF] Karlsson | Heart rate as a marker of stress in ambulance personnel: a pilot study of the body's response to the ambulance alarm[END_REF][START_REF] Hall | The acute physiological stress response to an emergency alarm and mobilization during the day and at night[END_REF], and an increase in salivary cortisol concentrations [START_REF] Hall | The acute physiological stress response to an emergency alarm and mobilization during the day and at night[END_REF]. The second phase, the fire suppression phase, corresponds to the phase of firefighting activities, such as forcible entry, search and rescue operations or extinguishing a fire [START_REF] Kales | Firefighters and on-duty deaths from coronary heart disease: a case control study[END_REF]. During this phase, firefighters engage in intense physical activity in psychologically stressful situations with high temperatures. This leads to high, and sometimes maximal, HR, and to an increase in BP, body temperature and psychological stress [START_REF] Barr | The thermal ergonomics of firefighting reviewed[END_REF][START_REF] Boisseau | Air management and physiological responses during simulated firefighting tasks in a high-rise structure[END_REF][START_REF] Horn | Physiological recovery from firefighting activities in rehabilitation and beyond[END_REF][START_REF] Windisch | Physiological Responses to Firefighting in Extreme Temperatures Do Not Compare to Firefighting in Temperate Conditions[END_REF][START_REF] Ravier | Physiological responses and parasympathetic reactivation in rescue interventions: The effect of the breathing apparatus[END_REF][START_REF] Wilkinson | Physiologic strain of SCBA confidence course training compared to circuit training and live-fire training[END_REF]. The third phase, the alarm return phase, corresponds to the several hours following a fire suppression. During this period, the psychophysiological stress generated by the intervention remains, and it can sometimes take several hours for the physiological parameters to return to initial levels. After simulated firefighting activities, core temperature continues to increase for many minutes [START_REF] Selkirk | Active versus passive cooling during work in warm environments while wearing firefighting protective clothing[END_REF][START_REF] Horn | Physiological recovery from firefighting activities in rehabilitation and beyond[END_REF], and the HR returns to baseline values only after about 80 minutes [START_REF] Horn | Physiological recovery from firefighting activities in rehabilitation and beyond[END_REF]. Furthermore, a significant acute parasympathetic perturbation has been observed after simulated firefighting activities [START_REF] Ravier | Physiological responses and parasympathetic reactivation in rescue interventions: The effect of the breathing apparatus[END_REF]. Indeed, in this study, we observed a greater vagal depression was observed after a simulated emergency than after an incremental running test performed until exhaustion.

The amount of stress during a fire the interventions can represent major issues for firefighters on two levels.

First, for firefighters with underlying cardiovascular disease, a significant amount of stress can induce pathophysiological changes causing a risk of death [START_REF] Smith | Cardiovascular strain of firefighting and the risk of sudden cardiac events[END_REF][START_REF] Kales | Firefighting and the heart: implications for prevention[END_REF]. Second, regular exposure to a source of stress could contribute to the long-term development of cardiovascular disease [START_REF] Steptoe | Stress and cardiovascular disease[END_REF]. Thus, despite a high level of exposure to traumatic risks [START_REF] Kazemi | Comparison of melatonin profile and alertness of firefighters with different work schedules[END_REF], sudden cardiac events are the leading cause of line-of-duty death for firefighters in the United States [START_REF] Kales | Emergency duties and deaths from heart disease among firefighters in the United States[END_REF][START_REF] Smith | Cardiovascular strain of firefighting and the risk of sudden cardiac events[END_REF]. Consequently, the comparison of a day and night intervention would determine whether or not firefighters' performance and psychophysiological stress are affected by the time period in which the intervention occurs, considering that an increase in cardiovascular stress is associated with adverse outcomes for the health of firefighters [START_REF] Smith | Cardiovascular strain of firefighting and the risk of sudden cardiac events[END_REF][START_REF] Kales | Firefighting and the heart: implications for prevention[END_REF].

Finally, the sudden increase in HR and BP in response to the emergency alarm increases the risk of death among firefighters [START_REF] Kales | Firefighters and on-duty deaths from coronary heart disease: a case control study[END_REF][START_REF] Kales | Emergency duties and deaths from heart disease among firefighters in the United States[END_REF]. A previous study showed that in comparison to a classical emergency alarm, a gentle awakening carried out by an experimenter mitigated the increase in HR [START_REF] Hall | The acute physiological stress response to an emergency alarm and mobilization during the day and at night[END_REF].

Usually, the alarm signal is a sound of at least 85 db(A) emitted by a transmitter carried by the firefighter.

Recently, the Regional Fire and Rescue Service offered to some firefighters a modified transmitter that starts by vibrating for 30 seconds, before emitting a sound signal if the transmitter is not turned off. The objective of this device is to reduce the stress of the firefighters during the alarm. Therefore, it is important to measure its effectiveness in workplace ecological conditions, to guide firefighters in their choice of alarms.

Consequently, the present field study aimed to: (1) compare the daytime and night-time physiological and psychological responses of structural firefighters to a simulated emergency; (2) compare the physiological and psychological responses of structural firefighters to a sound alarm and a vibration alarm, at night. It was hypothesised that the night intervention would exhibit higher physiological response than the day intervention, and that this higher response could be attenuated by a less noisy alarm.

Materials and methods

Participants

Sixteen male firefighters participated in this study (Table 1). All the participants had been medically screened by the local firefighter's healthcare institution, and each had received medical clearance to engage in firefighting activities. Prior to testing, all the participants gave their voluntary written informed consent, which indicated the purpose, the benefits and the risks of the investigation and the right to withdraw from participation at any time.

This study was conducted in accordance with the recommendations of the 1964 Declaration of Helsinki and its later amendments. The research design was examined and approved by the medical service and the Institutional Review Board of the Regional Fire and Rescue Service. ml⋅min -1 ⋅kg -1 18.6 ± 5.9 years

Experimental design

The study was conducted at the participants' workplace, and the rescue intervention was part of their occupational activity. The experimental exercises were part of the firefighters' regular training exercises. Prior to the experimental sessions, during a familiarisation session, the procedures were thoroughly explained, and the participants tested the connected suit and the psychological questionnaires used in the experimental sessions.

The connected suit used in this study was that of the Hexoskin brand (Hexoskin® Carré Technologies Inc., Montreal, Canada). Next, the participants completed the Intermittent Fitness Test [START_REF] Buchheit | The 30-15 intermittent fitness test: accuracy for individualizing interval training of young intermittent sport players[END_REF] to determine their individual HR peak (HRmax). The V O was estimated based upon the participant's final running speed using the following formula [START_REF] Buchheit | The 30-15 intermittent fitness test: 10 year review[END_REF]) : V ̇O2max (ml⋅min -1 ⋅kg -1 ) = 28.3 -(2.15 x G) -(0.741 x A) -(0.0357 x W) + (0.0586 x A x VIFT) + (1.03 x VIFT) where: VIFT is the final running speed, G is gender (male = 1), A is age (in years) and W is weight (in kilograms). Then, all the participants performed the three experimental conditions in a randomised order, interspersed by a minimal minimum of 3 days and a maximum of 14 days. The firefighters completed the same simulated rescue intervention (Figure 1) under three different For the DaySA condition, the participants completed a 10-minute sitting rest period at 08:00 h in a quiet room at ambient temperature (~20°C) in order to perform the resting measurements. Then, at 08:30 h, they went to a bedroom that was assigned to them for the duration of the study. In the bedroom, they rested without sleeping, lying down wearing the same attire they wear when sleeping at night in the fire station. The participants were informed that they might hear an alarm for the simulated rescue intervention at any time of the morning. At 09:00 h, the alarm signal was triggered. It was issued by a transmitter assigned to the firefighter and usually used for real interventions. The alarm was placed on a table next to the bed, at a distance of about 1 meter from the firefighter. The sound of the signal was about 85 db(A). Upon hearing the signal, the firefighters had to get dressed and go to the locker room as quickly as possible. The time between the triggering of the alarm and the arrival in the locker room corresponds to the alarm mobilisation phase. Once in the locker room, the pre-simulated intervention measures were carried out for 5 minutes, and the participants were equipped with the protective equipment for the simulated rescue intervention. The personal protective equipment consisted of a helmet, gloves, a bunker coat and pants, boots and a self-contained breathing apparatus with an air cylinder and facial mask, for a total weight of approximately 22 kg. For breathing at a standard rate of 40 L⋅min -1 , the SCBA cylinder used in the study can provide 45 minutes of air. Under their personal protective equipment, the firefighters wore the standard clothing provided by the service, namely long pants and t-shirts. Once equipped and ready, all the participants performed the simulated rescue intervention as quickly as possible. When the firefighters finished the simulated rescue intervention, they had 1 minute to remove their personal protective equipment (SCBA, helmet, jacket) before completing a 10-minute resting period in a seated position in a quiet room at ambient temperature (~20°C). For the NightSA and the NightVA conditions, the resting measurements were completed at 22:00 h in the same room as in the DaySA condition. Then, the participants went into the same bedroom that was used for the daytime simulation, between 22:30 h and 23:30 h, depending on their habits. They were informed that they might hear an alarm for the simulated rescue intervention at any time during the night.

The alarm signal was triggered approximately 2 hours after the bedtime that was indicated by the firefighter, between 00:30 h and 01:30 h. Particular care was taken to ensure that the participants were sleeping deeply when the alarm sounded. We asked them in what state they were at the time of the alarm (sleeping, sleepy, awake) and if they were awake or sleepy the experiment was postponed for a different night. The same transmitter and the same sound were used for the NightSA condition and the DaySA condition. For the NightVA condition, the transmitter signal was modified so that it would only vibrate for 30 seconds. At the end of the 30 seconds, if the firefighter did not turn off the transmitter, a sound signal was added to the vibrations. Then, the whole protocol during the NightVA condition was were the same as that used in the NightSA condition (Figure 1). Again, we have ensured that the participants were woken only by the vibrations. If it was is the sound that woke them up, then the experiment was postponed for a different night.

The three experimental conditions were performed in a randomised order. For the three conditions, everything was done to allow for maximum uncertainty, as in real conditions. The study was conducted at the participants' workplace, it was part of their occupational activity and they could be called either for the simulated rescue intervention or for real interventions. In addition, several nights were recorded with the Hexoskin® suit, during which they were warned that they could be awakened, without us actually doing so. The participants were also asked to abstain from consuming caffeine 3 hours before testing and from engaging in high intensity exercise and consuming alcohol 24 hours before the tests. All the participants were familiar with the simulated rescue intervention and the fitness test because both had been part of their occupational skills training and the regular monitoring of their physical abilities. Indeed, once a year, the firefighters of the regional fire service perform physical tests: the incremental running test and also measurements of muscular endurance, flexibility, etc. These tests are then reviewed by the hierarchy and the health service. Finally, the simulated intervention is carried out regularly by the firefighters (i.e. several times a year), as part of their training exercises. heart rate variability; BP: blood pressure

Data analysis

Assessment of the firefighting performance

For both the alarm mobilisation phases and the simulated rescue interventions, the completion time (CT) was recorded manually using a manual chronometer. For the alarm mobilisation phase, the time trial began when the alarm was triggered; it ended when the firefighters entered the locker room. For the simulated rescue intervention, the time trial started at the beginning of the first task; it ended when the firefighter crossed the finish line. Air consumption was quantified in bars directly from the pressure recorded on the manometer of the self-contained breathing apparatus at the start and the end of the simulated rescue intervention. The accuracy of the pressure gauge was ± 5 bars.

Assessment of the physiological parameters

The participants were fitted with a connected suit during the three experimental conditions and during the Intermittent Fitness Test. The connected suit provided an electrocardiogram signal at a frequency of 256 Hz from three electrodes (two on the chest, one on the right supra iliac region). The data that were recorded using the Hexoskin® suit were shown to be reliable and valid under a laboratory condition [START_REF] Elliot | Validity and reliability of the Hexoskin wearable biometric vest during maximal aerobic power testing in elite cyclists[END_REF]). Then, HR was calculated at 1 Hz, and was analysed during three distinct periods. During the alarm mobilisation phase, the pre-alarm HR corresponded to the average HR of the previous 5 seconds before the alarm signal, the peak HR was the maximal HR reached during the phase and the HR reactivity was calculated as the difference between peak HR and pre-alarm HR. For the alarm mobilisation phase, the pre-alarm HR, the peak HR and the HR reactivity were expressed in beats⋅min -1 . Then, mean and peak HR were determined for the entire simulated rescue intervention. For the simulated rescue intervention, mean and peak HR were expressed as the percentage of the maximal HR measured during the Intermittent Fitness Test (% HRmax). Finally, during the recovery period, HR recovery (HRR) was calculated by taking the difference between the exercise final HR and the HR at 60 seconds after the end of the exercise (HRR60s). Thus, a short-term HR time constant, a T30 index, was determined as the negative reciprocal of the slope of the regression line for the first 30 seconds (-1/ slope). Since for a few seconds after high intensity exercise, HR can continue to rise or plateau, we actually calculated the T30 from the 10 th to the 40 th seconds of recovery, as previously recommended [START_REF] Peçanha | Methods of assessment of the post-exercise cardiac autonomic recovery: a methodological review[END_REF]. It has been demonstrated that the HRR60s and T30 indices reflect parasympathetic reactivation immediately after exercise [START_REF] Peçanha | Methods of assessment of the post-exercise cardiac autonomic recovery: a methodological review[END_REF].

HR variability (HRV) derived from the electrocardiogram signal extracted from the Hexoskin® suit was recorded 10 minutes after the simulated rescue interventions. R-R intervals were analysed both on time-and frequency-domains using Kubios software (Kubios HRV Analysis v3.0; Bio-signal Analysis and Medical

Imaging Group at the Department of Applied Physics, University of Kuopio, Kuopio, Finland), and the signal was corrected automatically using software correction with a medium threshold of correction. After a 5-minute period of stabilisation, HRV analysis was performed for a 5-to-10-minute period, post-exercise. In the frequency domain, HRV was analysed using spectral analysis of the intervals from the fast Fourier transform. The high frequency (HF, ms 2 ) band, ranging between 0.15 Hz and 0.40 Hz, was selected for this study as the index to evaluate the post-exercise parasympathetic nervous system reactivation. Post-exercise vagal modulations were also assessed in the time domain by calculating the root mean square of successive differences of normal R-R interval (RMSSD, ms) and the standard deviation of instantaneous beat-to-beat R-R interval variability derived from the Poincare ́ Plot analysis (SD1, ms) indices.

Arterial systolic and diastolic BP were assessed via auscultation on the left upper arm while passively supporting the lower arm. In each condition, the participants' BP was assessed at the end of the resting measures, during the pre-simulated intervention measures, within the first minute of the post-simulated intervention and at the 10minute post-simulated intervention.

Assessment of the psychological parameters

The firefighters' anxiety and self-confidence levels were measured using a French adaptation [START_REF] Cury | Mesurer l'anxiété du sportif en compétition: Présentation de l'échelle d'état d'anxiété en compétition (EEAC)[END_REF] of the Competitive State Anxiety Inventory-2 (CSAI-2) questionnaire [START_REF] Martens | Longer exercise duration delays post-exercise recovery of cardiac parasympathetic but not sympathetic indices[END_REF]). This questionnaire consists of 27 items related to feelings of cognitive anxiety, somatic anxiety and self-confidence. In each of the study conditions, all the participants completed the questionnaire during the resting measures and during the presimulated intervention measures. Then, sleepiness was assessed during the resting and pre-simulated intervention measures using the Stanford Sleepiness Scale (SSS) [START_REF] Herscovitch | Sensitivity of the Stanford sleepiness scale to the effects of cumulative partial sleep deprivation and recovery oversleeping[END_REF]. Finally, the rating of perceived exertion (RPE) was self-evaluated 10 minutes after the end of the simulated rescue intervention by using the category ratio scale.

Statistical analysis

All data were expressed as mean ± standard-deviation (SD). The normality for data distribution and the equality of variance between the samples were checked with Shapiro-Wilk's test and Bartlett's test, respectively. Because the RMSSD and the HF indices were not normally distributed, the data were log-transformed (lnRMSSD and lnHF). The differences between the DaySA and the NightSA conditions and the differences between the NightSA and the NightVA conditions were analysed using pairwise t-tests if the data were normally distributed (for CT, air consumption, HR, T30, HRR60s, lnRMSSD, lnHF and SD1) or Wilcoxon tests if the data were not normally distributed (for the psychological parameters and BP values). To account for the increased possibility of a type-I error, the Bonferroni correction was used to adjust for multiple statistical tests (VanderWeele and Mathur 2019).

Friedman tests were used to analyse the BP differences between time measures (Resting-, Pre-, Post-1 min, post-10 min measures) and the Nemenyis procedure was used when the null hypothesis was rejected. Statistical analysis was performed using XLSTAT software 2013 (Addinsoft SARL, Paris, France). Statistical significance was set at <0.05. The magnitude of the differences was interpreting using Cohen's d effect-size where <0.20 is trivial, 0.20 to 0.49 is small, 0.50 to 0.79 is moderate and >0.80 is large [START_REF] Cohen | Heart-rate recovery immediately after exercise as a predictor of mortality[END_REF]).

Results

Performance and physiological parameters

The alarm was triggered at 08:32 h ± 00:07 h for the DaySA condition, at 00:50 h ± 00:17 h for the NightSA condition and at 00:53 h ± 00:16 h for the NightVA condition.

For the three experimental conditions, the CT and HR responses for both the alarm mobilisation phase and the simulated rescue intervention are presented in Table 2. The cardiac parasympathetic indices of the acute recovery phase for the three conditions are also displayed in Table 2. Systolic BP and diastolic BP for the three experimental conditions are presented in Figure 3. There was a significant difference between the pre-and 1-min post-simulated intervention systolic BP in comparison to resting systolic BP for both the three conditions, but no difference was found between the conditions.

Psychological parameters

Post-simulated intervention RPE was not significantly different between the DaySA and NightSA conditions (7.4 ± 2.1 and 8.1 ± 2.2 respectively). The post-simulated intervention RPE was 8.1 ± 1.7 for the NightVA condition, which was not significantly different from the NightSA condition.

Differences between the resting and pre-simulated intervention values of the CSAI-2 and SSS questionnaires are presented in Table 3. The comparison of the DaySA and NightSA conditions revealed a higher level of presimulated intervention sleepiness (p <0.0001) and a lower level of pre-simulated intervention self-confidence (p <0.01) for the NightSA condition in comparison to the DaySA condition. The comparison revealed no differences between the NightSA and NightVA conditions.

Discussion

This study aimed to assess the psychophysiological responses of firefighters throughout a simulated rescue intervention performed during the day and at night, in workplace ecological conditions. Furthermore, the study aimed to determine if a modified vibrating alarm has an impact on these psychophysiological responses during a simulated intervention performed at night. The main results revealed that during the alarm mobilisation phase, the HR reactivity was higher during the intervention performed at night than the intervention performed during the day, and it can be decreased with the use of a vibrating alarm during the night. During the simulated rescue intervention, no differences in the firefighters' performance and HR responses were found between the day and the night conditions or between the two different alarm signals. However, the cardiac parasympathetic reactivation following the simulated intervention was lower during the night condition than during the day condition. In terms of the psychological responses, the level of sleepiness was higher, and the level of selfconfidence was lower before the night-simulated intervention than before the day-simulated intervention. Presimulated intervention somatic anxiety increased in comparison to the resting measures for both the day and night conditions, but no differences were found between the two conditions.

Firstly, during the alarm mobilisation phase, HR reactivity was higher in the NightSA condition than in the DaySA condition (77.2 ± 20.4 vs 65.1 ± 17.9 beats⋅min -1 respectively). In our study, the HR reactivity measured during the day was slightly higher than those measured in previous studies, i.e. 20 to 61 beats⋅min -1 [START_REF] Kuorinka | Firefighters' reaction to alarm, an ECG and heart rate study[END_REF][START_REF] Karlsson | Heart rate as a marker of stress in ambulance personnel: a pilot study of the body's response to the ambulance alarm[END_REF][START_REF] Hall | The acute physiological stress response to an emergency alarm and mobilization during the day and at night[END_REF]. In our study, in the DaySA condition, although the participants were not asleep, they rested in a supine position for about 30 minutes wearing the same attire that was worn in the NightSA condition. Consequently, the recorded pre-alarm HR was lower in our study than in previous studies, which could explain our higher HR reactivity. Only one study analysed HR reactivity in a night condition, and it found lower HR reactivity values than those measured in our study for the NightSA condition [START_REF] Hall | The acute physiological stress response to an emergency alarm and mobilization during the day and at night[END_REF]. These authors also compared HR reactivity during a day and a night alarm mobilisation phase and showed no significant differences. In our study, the higher HR reactivity in the NightSA condition in comparison to the DaySA condition was due to a significantly lower pre-alarm HR in the NightSA condition; the peak HR was not different between the day and night conditions. It is well established that resting HR is influenced by circadian variations, and the lowest values are obtained between 01:00 h 02:00 h [START_REF] Harma | Circadian variation of physiological functions in physically average and very fit dayworkers[END_REF], as found in our study. Moreover, participants were asleep in the night condition but not in the day condition. This could also influence the resting HR, which is lower when a person is sleeping [START_REF] Viola | Sleep processes exert a predominant influence on the 24-h profile of heart rate variability[END_REF].

Therefore, the circadian rhythmicity of the resting HR as well as the HR during waking state when waking up, could explain the different HR reactivity found between the NightSA and the DaySA conditions. Moreover Finally, the alarm mobilisation phase resulted in an increase in pre-intervention systolic BP in comparison to the resting BP values, with no difference between the NightSA and the DaySA conditions. Both the significant increase in HR and the increase of pre-intervention systolic BP were in accordance with the "fight or flight" reaction of firefighters during the alarm mobilisation phase, as described in previous studies [START_REF] Hall | The acute physiological stress response to an emergency alarm and mobilization during the day and at night[END_REF][START_REF] Smith | Cardiovascular strain of firefighting and the risk of sudden cardiac events[END_REF].

Secondly, regarding the simulated rescue intervention, our results revealed no difference between the NightSA and the DaySA conditions for the CT, HR and BP responses. As presented in Table 2, depending on the condition, mean HR ranged between 85% and 86% of HRmax and peak HR ranged between 90% and 91% of HRmax. These results are similar to those reported by previous studies with simulated firefighting activities [START_REF] Williams-Bell | Physiological demands of the firefighter candidate physical ability test[END_REF][START_REF] Windisch | Physiological Responses to Firefighting in Extreme Temperatures Do Not Compare to Firefighting in Temperate Conditions[END_REF][START_REF] Ravier | Physiological responses and parasympathetic reactivation in rescue interventions: The effect of the breathing apparatus[END_REF]). Moreover The increase in systolic BP during the simulated rescue intervention (Figure 2) was higher in our study than in a previous study [START_REF] Horn | Physiological recovery from firefighting activities in rehabilitation and beyond[END_REF].

However, in contrast to our study, in the previous research [START_REF] Horn | Physiological recovery from firefighting activities in rehabilitation and beyond[END_REF], the firefighting activity was longer (i.e. 18 minutes) and it included rest periods, which can decrease the systolic BP. The HR and BP reported in our study showed that the simulated rescue intervention was a strenuous exercise. Otherwise, to the best of our knowledge, our study is the first to compare day-and night-simulated rescue interventions in firefighters.

Although the results of studies with healthy subjects have revealed discrepancies, previous findings reported no effect of circadian rhythm on physical performance or physiological responses (V O , HR) during submaximal exercise [START_REF] Reilly | Investigation of circadian rhythms in metabolic responses to exercise[END_REF][START_REF] Deschenes | Chronobiological effects on exercise performance and selected physiological responses[END_REF] or maximal exercise [START_REF] Deschenes | Chronobiological effects on exercise performance and selected physiological responses[END_REF]. Regular training at specific times of the day can influence the diurnal rhythm by limiting the differences between the evening and morning performances [START_REF] Chtourou | The effect of training at a specific time of day: a review[END_REF]. Because their shift is 24 hours long, firefighters have to deal with regular interventions at any time of the day or night. Consequently, this regular training may help firefighters perform equally well at night and during the day. Moreover, firefighting activities are a physical stressor and a psychological stressor [START_REF] Robinson | Stress reactivity and cognitive performance in a simulated firefighting emergency[END_REF]. In response to a stressful situation, the hypothalamic-pituitary-adrenal axis releases cortisol, which allows the body to be on high alert and which may enhance the physical response to an emergency. The cortisol production follows a circadian rhythmicity, but it also includes an adaptive response to the acute stress that firefighters experience before simulated interventions [START_REF] Robinson | Stress reactivity and cognitive performance in a simulated firefighting emergency[END_REF] or during the alarm mobilisation phase [START_REF] Jay | Can stress act as a sleep inertia countermeasure when on-call?[END_REF]). In our study, for both the NightSA and the DaySA conditions, peak HR was similar during the alarm mobilisation phase, and there was a similar increase in pre-intervention somatic anxiety (Table 3). These results reveal that the firefighters were in a physically and psychologically stressful situation during the daytime and night-time interventions. Although the adaptive response of the cortisol production was not measured in our study, it may have helped the firefighters perform as well as during the NightSA condition and the DaySA condition.

Thirdly, the present study aimed to investigate cardiac parasympathetic reactivation after a simulated rescue intervention conducted at night and during the day. In a previous study, we investigated cardiac parasympathetic reactivation after firefighting activities [START_REF] Ravier | Physiological responses and parasympathetic reactivation in rescue interventions: The effect of the breathing apparatus[END_REF]), but to the best of our knowledge, no studies have evaluated it at night. In the present study, the indices of cardiac parasympathetic reactivation were higher than those that were observed previously (e.g. HRR60s, LnRMSSD), which suggests a greater cardiac parasympathetic reactivation in the current study. This difference could be due to the exercise duration, which was longer in the earlier study than in the present experiment (i.e. 13.4 ± 2.1 min vs 4.2 ± 0.6 min) [START_REF] Ravier | Physiological responses and parasympathetic reactivation in rescue interventions: The effect of the breathing apparatus[END_REF]). Indeed, previous research studies have shown that a longer exercise duration may attenuate the post-exercise HRV indices of cardiac parasympathetic reactivation [START_REF] Martens | Longer exercise duration delays post-exercise recovery of cardiac parasympathetic but not sympathetic indices[END_REF]). Nevertheless, despite the short duration of the simulated rescue intervention in the present study, the recovery indices values are similar to those observed after high-intensity exercises in sports [START_REF] Buchheit | Parasympathetic reactivation after repeated sprint exercise[END_REF][START_REF] Nakamura | Cardiac autonomic responses to repeated shuttle sprints[END_REF].

Furthermore, while the intensity and the duration were similar between the night-and the day-simulated rescue interventions, the cardiac parasympathetic activity was lower in the NightSA condition than in the DaySA condition. Few studies have investigated the effect of the time of day on acute post-exercise recovery, with inconsistent results. Some studies reported a lower HR recovery after evening exercise in comparison to morning exercise in heathy subjects [START_REF] Cohen | Human orcadian rhythms in resting and exercise pulse rates[END_REF]. However, other studies found no differences in acute recovery after morning and night exercise [START_REF] Harma | Circadian variation of physiological functions in physically average and very fit dayworkers[END_REF][START_REF] Prodel | Different times of day do not change heart rate variability recovery after light exercise in sedentary subjects: 24 hours Holter monitoring[END_REF]. A higher post-exercise blood lactate concentration would be one possible explanation for the depressed cardiac parasympathetic recovery during the night. Previous studies have reported a circadian variation in blood lactate values after exercises performed at the same intensities [START_REF] Baxter | Influence of time of day on all-out swimming[END_REF][START_REF] Deschenes | Chronobiological effects on exercise performance and selected physiological responses[END_REF], and it has been shown that the blood lactate concentration was associated with a decrease in cardiac parasympathetic reactivation [START_REF] Buchheit | Parasympathetic reactivation after repeated sprint exercise[END_REF]). It has also been reported that the aerobic contribution during a Wingate test was lower in the morning than in the afternoon [START_REF] Souissi | Effect of time of day on aerobic contribution to the 30-s wingate test performance[END_REF]). The number of cardiovascular events for the United States firefighters is related to the distribution of interventions; in the general population, it follows a circadian rhythm [START_REF] Kales | Firefighters and on-duty deaths from coronary heart disease: a case control study[END_REF]. The risk of death by coronary heart disease is 10-fold higher during the recovery period after firefighting interventions than during non-emergency duties [START_REF] Kales | Firefighters and on-duty deaths from coronary heart disease: a case control study[END_REF]. Because weak post-exercise parasympathetic activity is associated with an increased risk of death [START_REF] Cohen | Heart-rate recovery immediately after exercise as a predictor of mortality[END_REF][START_REF] Lahiri | Assessment of autonomic function in cardiovascular disease[END_REF], the impaired parasympathetic reactivation after firefighting activities might be one cause of the increased risk of firefighters' death. Finally, all of these results should be considered in the context of the development of stress at work. Indeed, firefighters face many stressful situations, as shown through the HR reactivity during the intervention or through the post-exercise vagal depression. In addition, it has recently been shown that the nocturnal HRV of firefighters is reduced while on-call (Marcel-Millet et al. 2020a). All of these elements can lead to a chronic reduction in HRV in firefighters who experience high job stress, as shown by [START_REF] Shin | Factors related to heart rate variability among firefighters[END_REF]. Moreover, high levels of work stress have been shown to affect the development of cardiovascular disease [START_REF] Belkic | Is job strain a major source of cardiovascular disease risk?[END_REF][START_REF] Steptoe | Stress and cardiovascular disease[END_REF]. This is why emergency services should consider implementing strategies to reduce the different sources of stress for firefighters. Among the different strategies that can be adopted, improving the reactivation of the parasympathetic system should be considered. Active cooling strategies, such as hand and forearm immersion, have been proposed to decrease the cardiovascular and thermoregulatory strain of firefighters [START_REF] Selkirk | Active versus passive cooling during work in warm environments while wearing firefighting protective clothing[END_REF][START_REF] Barr | The impact of different cooling modalities on the physiological responses in firefighters during strenuous work performed in high environmental temperatures[END_REF]. Regarding HRV, both face and body cold water immersion improved cardiac parasympathetic reactivation, in particular thanks to a decrease in the core temperature [START_REF] Haddad | Influence of cold water face immersion on postexercise parasympathetic reactivation[END_REF][START_REF] De Oliveira Ottone | The effect of different water immersion temperatures on post-exercise parasympathetic reactivation[END_REF]. In hot conditions, these strategies are necessary to increase exercise tolerance and prevent the firefighters' exhaustion [START_REF] Selkirk | Active versus passive cooling during work in warm environments while wearing firefighting protective clothing[END_REF]).

In addition, to reduce the stress of firefighters, the second objective of this study was to compare two different types of alarms during the night. The results revealed that the modification of the night alarm signal with a vibrating alarm, which was a softer alarm than the sound alarm, decreased cardiac stress during the alarm mobilisation phase. Indeed, between the NightSA and the NightVA conditions, the pre-alarm HR was similar but HR reactivity in the alarm mobilisation phase was lower in the NightVA condition than in the NightSA condition.

Similar results were observed in a previous study, which revealed a lower HR reactivity when participants were gently awakened in comparison to using a sound alarm signal [START_REF] Hall | The acute physiological stress response to an emergency alarm and mobilization during the day and at night[END_REF]. However, that study [START_REF] Hall | The acute physiological stress response to an emergency alarm and mobilization during the day and at night[END_REF]) modified the alarm signal and the subsequent mobilisation, which implied a lower physical activity in the mobilisation phase. Nevertheless, the significant increase in HR during the alarm mobilisation phase could be due to both the alarm stress and the subsequent movements [START_REF] Hall | The acute physiological stress response to an emergency alarm and mobilization during the day and at night[END_REF]. The stress related to the alarm signal seems to contribute significantly to the HR responses, as shown previously in a study with ambulance personnel [START_REF] Karlsson | Heart rate as a marker of stress in ambulance personnel: a pilot study of the body's response to the ambulance alarm[END_REF]. A change in a night alarm signal seems sufficient to decrease the cardiac stress related to the emergency alarm. Moreover, no difference was observed between the NightSA and the NightVA conditions for all the other parameters, such as CT and HR, for the simulated rescue intervention and the indices of cardiac parasympathetic reactivation. The triggering of the alarm leads to a "fight or flight" reaction with a prominent sympathetic activation, a massive release of catecholamines and an increased HR [START_REF] Smith | Cardiovascular strain of firefighting and the risk of sudden cardiac events[END_REF].

These elements can be the cause of the significant increase in the risk of death during the alarm response [START_REF] Kales | Firefighters and on-duty deaths from coronary heart disease: a case control study[END_REF][START_REF] Kales | Emergency duties and deaths from heart disease among firefighters in the United States[END_REF]. In this context, it would be very interesting for the emergency services to provide firefighters with a modified alarm signal, which could decrease their cardiac stress during the alarm mobilisation phase.

Finally, regarding the psychological measures, the level of pre-intervention sleepiness was higher in the NightSA condition than in the DaySA condition. We also found this difference when we compared the resting measures:

the level of pre-intervention sleepiness increased during the night condition, but not during the day condition (Table 3). These results support the findings of previous studies that indicated that sleepiness followed a circadian rhythmicity, with a peak in sleepiness between 03:00 h and 07:00 h [START_REF] Valdez | Focus: Attention Science: Circadian Rhythms in Attention[END_REF]. This circadian pattern of sleepiness may be related to the melatonin secretion rhythm, which increases during the night [START_REF] Kazemi | Comparison of melatonin profile and alertness of firefighters with different work schedules[END_REF]. Another possible explanation of the increase in sleepiness may be the sleep restriction generated by the simulated rescue intervention [START_REF] Philip | Acute versus chronic partial sleep deprivation in middle-aged people: differential effect on performance and sleepiness[END_REF]. Moreover, we found no difference in the level of sleepiness between the NightSA and NightVA conditions. This result is in accordance with the study by [START_REF] Jay | Can stress act as a sleep inertia countermeasure when on-call?[END_REF], who revealed that a less disruptive awakening did not alter the participants' sleepiness after waking. These are important findings considering that firefighters have to "mobilise", drive and make decisions just after waking up [START_REF] Jay | Can stress act as a sleep inertia countermeasure when on-call?[END_REF].

We found a significant difference in the pre-intervention self-confidence between the NightSA and the DaySA conditions. When compared to the resting measures, the participants' level of self-confidence decreased during the night condition but not during the day condition (Table 3). A positive linear relationship between selfconfidence and sports performance was found in previous studies [START_REF] Woodman | The relative impact of cognitive anxiety and self-confidence upon sport performance: A meta-analysis[END_REF]. However, other factors moderated this relationship, such as sex and competitive standards [START_REF] Woodman | The relative impact of cognitive anxiety and self-confidence upon sport performance: A meta-analysis[END_REF], which may explain the lack of difference in our study between the firefighters' daytime and night-time performances, although they had lower self-confidence during the night. Nevertheless, it is important for firefighters to consider this decrease in self-confidence because they can be faced with very mentally challenging situations.

In terms of anxiety, the somatic anxiety was higher during the pre-intervention measures than during the resting measures under the day and night conditions, but no differences were found between the conditions (Table 3).

Somatic anxiety was defined as "the physiological and affective elements of the anxiety experience that develop directly from autonomic arousal" (p.6) [START_REF] Martens | Longer exercise duration delays post-exercise recovery of cardiac parasympathetic but not sympathetic indices[END_REF]). Consequently, the increase in somatic anxiety in our study was not surprising, with the activation of the sympathetic nervous system during the alarm mobilisation phase, as measured by the increase of HR (Table 2) and with the likely hypothalamic-pituitaryadrenal axis activation that was measured in previous studies [START_REF] Robinson | Stress reactivity and cognitive performance in a simulated firefighting emergency[END_REF][START_REF] Hall | The acute physiological stress response to an emergency alarm and mobilization during the day and at night[END_REF]). However, no difference was found for cognitive anxiety, which was defined by [START_REF] Martens | Longer exercise duration delays post-exercise recovery of cardiac parasympathetic but not sympathetic indices[END_REF] as "the mental component of anxiety and is caused by negative expectations about success or by negative self-evaluation" (p.6).

The participants in our study were familiar with the simulated rescue intervention, as it had been part of their occupational skills training. Consequently, they had no doubts about their ability to achieve it successfully.

However, it is reasonable to assume that during real interventions, when firefighters are confronted with unpredictable situations with sometimes vital issues, their level of cognitive anxiety may increase. Nevertheless, the increase in the level of somatic anxiety is an important result because it has been shown that there is a curvilinear relationship between somatic anxiety and sports performance [START_REF] Martens | Longer exercise duration delays post-exercise recovery of cardiac parasympathetic but not sympathetic indices[END_REF]). The increase in anxiety represents an important concern for the health of firefighters, who are significantly affected by coronary heart diseases [START_REF] Smith | Cardiovascular strain of firefighting and the risk of sudden cardiac events[END_REF]. It has been shown that anxiety may increase the risk of coronary heart diseases [START_REF] Kubzansky | Anxiety and coronary heart disease: a synthesis of epidemiological, psychological, and experimental evidence[END_REF]. Further studies are required to determine whether the performance and health of firefighters are related to anxiety or/and self-confidence.

There were several limitations to consider in this study. First, due to logistics issues, no women participated in this study although they represented 17 % of French firefighters in 2020. This may prevent the generalization of results to female firefighters, as gender may influence performance and physiological responses [START_REF] Williams-Bell | Physiological demands of the firefighter candidate physical ability test[END_REF], and as HRV may be influenced by the menstrual cycle [START_REF] Bai | Influence of the menstrual cycle on nonlinear properties of heart rate variability in young women[END_REF].

Second, the anthropometric data of the participants in this study diverge from the data usually published in firefighters' research, with a lower BMI and a higher estimated V ̇O2max in our study [START_REF] Selkirk | Active versus passive cooling during work in warm environments while wearing firefighting protective clothing[END_REF][START_REF] Boisseau | Air management and physiological responses during simulated firefighting tasks in a high-rise structure[END_REF][START_REF] Horn | Physiological recovery from firefighting activities in rehabilitation and beyond[END_REF][START_REF] Horn | Firefighter and fire instructor's physiological responses and safety in various training fire environments[END_REF]. The study being physically strenuous, it is the most athletic firefighters of the fire station who have volunteered to participate. This difference in fitness may affect the data of our study, a good physical condition allowing to improve the firefighters' performance [START_REF] Williams-Bell | Physiological demands of the firefighter candidate physical ability test[END_REF]Marcel-Millet et al. 2020b) without necessarily influencing cardiac parasympathetic reactivation (Marcel-Millet et al. 2020b).

Conclusions

In conclusion, the firefighters' cardiac stress in response to the alarm signal was greater during a night-simulated rescue intervention than during the day, and the cardiac parasympathetic reactivation in the post-simulated rescue intervention was more impaired in the night in comparison to the day. Moreover, the firefighters felt sleepier and less self-confident before the night-simulated intervention than before the day-simulated intervention. Nevertheless, the firefighters were equally efficient during the night-simulated intervention and the day-simulated intervention, with similar CT and HR responses between the two conditions. The use of a vibrating signal alarm during the night decreased the firefighters' cardiac stress throughout the alarm signal phase without influencing their subsequent performance, cardiac parasympathetic recovery and psychological arousal.

Regarding the applications of the present study, the emergency services should consider implementing strategies to improve parasympathetic reactivation after firefighting activities, especially at night when the disturbance is further increased. Hand and forearm immersion has been proposed as effective cooling strategy to decrease the physiological strain of firefighters [START_REF] Barr | The impact of different cooling modalities on the physiological responses in firefighters during strenuous work performed in high environmental temperatures[END_REF]).

  conditions: 1) during the day, in the morning, with a sound alarm signal (DaySA), 2) during the night with a sound alarm signal (NightSA) and 3) during the night with a vibrating alarm signal (NightVA). The simulated rescue intervention consisted of 5 tasks, without downtime: (a) Hoses: The participants carried two hoses (7 kg each) over flat ground for a distance of over 100 m; (b) Obstacles course: After setting down the hoses, the participants completed a 50-meter course that required them to crawl under obstacles; (c) Tower: The participants grabbed their hoses again, and dropped them on the 4th floor of a tower; (d) Mannequin: The participants used a strap to carry a 60 kg mannequin down one floor and then up one floor; (e) Hoses: Finally, the participants hoisted their hoses again before going down the 4 floors of the tower and returning to the starting point. During each session, the participants were asked to perform the simulated rescue intervention as quickly as possible; they were given verbal encouragement throughout the test.

Figure 1 .

 1 Figure 1. Overview of the experimental design. CSAI-2: Competitive State Anxiety Inventory -2; SSS:

  All the cardiac parasympathetic indices were lower in the NightSA condition in comparison to the DaySA condition. HR reactivity was lower in the DaySA condition in comparison to the NightSA condition (p <0.01) and was also lower in the NightVA condition in comparison to the NightSA condition (p <0.05). Air consumption during the simulated intervention was not significantly different between the DaySA and NightSA conditions(85.6 ± 19.7 and 78.8 ± 17.2 bars, respectively) and between the NightSA and NightVA (77.5 ± 14.8 bars) conditions.

  conditions for the HR at the end of the exercise. After 60 seconds of recovery, HR was higher in the NightSA condition than in the DaySA condition (p < 0.05).

Figure 2 .

 2 Figure 2. Heart rate (HR) recovery after the end of the exercise in the DaySA (day sound alarm), NightSA (night sound alarm) and NightVA (night vibrator alarm) conditions. * shows a significant difference between DaySA and NightSA with * p <0.05.

Figure 3 .

 3 Figure 3. Changes in systolic and in diastolic blood pressure (BP) throughout the DaySA (day sound alarm), NightSA (night sound alarm) and NightVA (night vibrator alarm) conditions. **: significant difference vs. rest < 0.01); ***: significant difference vs. rest (p < 0.001); #: significant difference vs. pre-intervention (p < 0.05); $$$: significant difference vs. 1-min post-intervention (p < 0.001).

Table 1 :

 1 Characteristics of the participants

	Age	Height	Weight	Body mass index	Estimated V ̇O2max	Work experience
	36.1 ± 5.8 years 175.3 ± 6.1 cm	73.6 ± 10.1 kg	kg/m 2 23.8 ± 1.7	55.8 ± 3.6

Table 2 .

 2 Performance, HR responses and parasympathetic reactivation indices for the three experimental conditions.

						DaySA vs. NightSA	NightSA vs. NightVA
	Phases	Variables	DaySA	NightSA	NightVA	ES (±95 CI)	ES (±95 CI)
						ES descriptor	ES descriptor
		CT mobilisation (s)	57.9 ± 26.6	104.9 ± 31.6*** 114.7 ± 27.8	1.61 (±0.82) Large	0.54 (±0.61) Medium
	Alarm	Pre-alarm HR (beats⋅min -1 )	58.6 ± 8.2	50.7 ± 4.5***	51.3 ± 8.1	1.18 (±0.77) Large	0.09 (±0.60) Trivial
	mobilisation	Peak HR (beats⋅min -1 )	123.7 ± 18.4	127.9 ± 20.3	116.1 ± 21.7	0.22 (±0.72) Small	0.57 (±0.61) Medium
		HR reactivity (beats⋅min -1 )	65.1 ± 17.9	77.2 ± 20.4**	64.7 ± 19.5 #	0.63 (±0.73) Medium	0.63 (±0.61) Medium
		CT intervention (s)	251.8 ± 38.6	257.6 ± 50.1	254.7 ± 33.2	0.13 (±0.72) Trivial	0.07 (±0.60) Trivial
	Simulated intervention	Mean HR (% HRmax)	86.0 ± 4.0	85.2 ± 4.7	84.3 ± 4.0	0.19 (±0.72) Trivial	0.21 (±0.60) Small
		Peak HR (% HRmax)	90.6 ± 2.9	89.6 ± 3.4	89.6 ± 2.2	0.34 (±0.72) Small	0.01 (±0.60) Trivial
		T30 (s)	171.8 ± 71.4	251.1 ± 106.0*	217.3 ± 46.7	0.88 (±0.75) Large	0.41 (±0.61) Small
		HRR60s (beats⋅min -1 )	38.0 ± 12.2	31.6 ± 8.4*	31.7 ± 10.0	0.61 (±0.73) Medium	0.01 (±0.60) Trivial
	Acute recovery	lnRMSSD (ms)	2.46 ± 0.64	2.15 ± 0.47*	2.34 ± 0.47	0.56 (±0.73) Medium	0.42 (±0.61) Small
		SD1 (ms)	9.89 ± 5.93	6.73 ± 3.29*	8.07 ± 3.07	0.66 (±0.73) Medium	0.42 (±0.61) Small
		lnHF (ms 2 )	3.88 ± 1.47	2.85 ± 1.11*	3.04 ± 1.17	0.79 (±0.74) Medium	0.16 (±0.60) Trivial
	Mean ± SD are displayed for DaySA (day sound alarm), NightSA (night sound alarm) and NightVA (night vibrator
	alarm) conditions. CT: completion time; T30: short-term time constant; HRR60s: heart rate recovery at 60 sec
	post-exercise; LnRMSSD: natural logarithm of the root mean square of successive differences of normal R-R

intervals; LnHF: natural logarithm of high frequency power; SD1: standard deviation of instantaneous beat-tobeat R-R intervals variability derived from the Poincare ́ Plot analysis. *shows a significant difference vs. DaySA with * p <0.05, ** p <0.01 and *** p <0.001; # shows a significant difference vs. NightSA with # p <0.05.

Table 3 .

 3 Evolution of the psychological parameters (sleepiness, anxiety and self-confidence) from rest to presimulated intervention for the DaySA, NightSA and NightVA conditions.

		Condition	Rest	Pre-intervention	ES (±95 CI)	Evolution (%)	ES descriptor
	SSS (on 7)	DaySA NightSA NightVA	1.69 ± 1.01 2.13 ± 1.54 2.25 ± 1.24	1.81 ± 1.05 4.25 ± 1.73 ** 3.56 ± 0.96 **	0.12 (±0.72) 1.30 (±0.78) 1.18 (±0.77)	7 100 58	Trivial Large Large
	CSAI-2 Somatic Anxiety	DaySA NightSA	1.21 ± 0.27 1.24 ± 0.31	1.64 ± 0.47 *** 1.77 ± 0.60 ***	1.11 (±0.77) 1.11 (±0.77)	36 43	Large Large
	(on 4)	NightVA	1.29 ± 0.35	1.81 ± 0.68 **	0.96 (±0.75)	40	Large
	CSAI-2 Cognitive Anxiety	DaySA NightSA	1.20 ± 0.30 1.24 ± 0.23	1.12 ± 0.23 * 1.39 ± 0.42	0.30 (±0.72) 0.41 (±0.72)	-7 12	Small Small
	(on 4)	NightVA	1.24 ± 0.36	1.37 ± 0.39	0.35 (±0.72)	10	Small
	CSAI-2 Self-confidence	DaySA NightSA	3.53 ± 0.44 3.43 ± 0.41	3.54 ± 0.43 2.89 ± 0.67 ***	0.01 (±0.72) 0.97 (±0.75)	0 -16	Trivial Large
	(on 4)	NightVA	3.41 ± 0.52	2.88 ± 0.66 **	0.89 (±0.75)	-16	Large

Mean ± SD are displayed for DaySA (day sound alarm), NightSA (night sound alarm) and NightVA (night vibrator alarm) conditions at rest and pre-simulated interventions. ES: effect size; CI: confidence interval; CSAI-2: Competitive State Anxiety Inventory -2; SSS: Stanford Sleepiness Scale. Scores for the SSS were expressed on a 7-point Likert scale and scores for all the CSAI-2 items were expressed on a 4-point Likert scale. *show a significant difference vs. rest with *: p <0.05; **: p <0.01; ***: p <0.001.

Acknowledgments

We would like to acknowledge the firefighters for their participation in this study and their technical support. We also thank the institutional board of the Service Départemental d'Incendie et de Secours du Doubs for its support.

Prior to testing, all participants gave a voluntary written informed consent which indicates the purpose, the benefits and the risks of the investigation and the possibility to stop their participation at any time.

Funding sources

The study was part of the European Cross-border Co-operation Programme (Interreg France-Suisse 2014-2020), and it was supported by a grant from the European Funding for Regional Development (FEDER).

Conflict of interest

No conflicts of interest, financial or otherwise, are declared by the authors. The authors declare that the results of the study are presented clearly, honestly, and without fabrication, falsification, or inappropriate data manipulation.

Ethical approval

This study was conducted in accordance with the recommendations of the 1964 Declaration of Helsinki and its later amendments. The research plan was examined and approved by the medical service and the Institutional Review Board of the Regional Fire and Rescue Service of Doubs, and it was approved by the Ethics Committee of the responsible institutional department.

Informed consent