Hugo A Kerhervé

Leonie M Harvey

Alexander N Eagles

Chris Mclellan

Dale Lovell

Hugo Kerherve
email: hugo.kerherve@univ-rennes2.fr

Body composition influences blood pressure during submaximal graded test in women

This study aimed to determine whether body composition affected cardiovascular responses of normal, overweight and obese women by comparing heart rate (HR) and blood pressure (BP) during a graded submaximal treadmill exercise. Thirty five healthy non-smoking, premenopausal women (age 30.8±9.5 yr; height 1.66±0.05 m; weight 73.8±18.9 kg; body fat 36.2±9.5%; maximum oxygen uptake 33.5±8.1 mL•min•kg -1 ) volunteered for this study, and were classified into three groups based on BMI: normal weight (NOR; ≤24.9 kg•m 2 ), overweight (OVW; 25-29.9 kg•m 2 ) and obese (OBE; ≥30 kg•m 2 ). Participants performed a submaximal graded test at 30%, 40%, 50% and 60% of maximal oxygen uptake, during which HR, systolic BP (SBP), diastolic BP (DBP) and mean arterial pressure (MAP) were measured. At rest, participants of OBE group had higher BP than NOR and OVW. During the submaximal graded test, HR, SBP and MAP increased as a function of intensity. There were no group differences in HR, but greater SBP, DBP and MAP in OBE compared to NOR and OBW at all intensities except 60%. Overall, our study further contributes to underscore the importance of stress testing specifically to evaluate the increased risks apparently healthy obese women are placed at to developing diseases from the chronic exposure to raised BP, despite normal resting BP and HR responses during exercise.

Introduction

Hypertension is one of the most prevalent non-communicable diseases, affecting more than 1 in 5 people worldwide [1]. It is a significant predictor of cardiovascular risk characterised by abnormally elevated resting blood pressure (BP), typically diagnosed with systolic BP (SBP) above 140 mmHg and diastolic BP (DBP) above 90 mmHg. Chronic exposure to pressure overload can lead to pathologic cerebrovascular, retinovascular and cardiovascular trauma, as well as secondary functional impairments such as altered thermoregulation from impaired peripheral vasodilation.

Measuring BP during exercise is also used as a significant predictor of cardiovascular risk: despite being normotensive at rest, individuals exhibiting a hypertensive response to exercise (HRE; SBP>210 mmHg in men and 190 mmHg in women) are at an increased risk of developing hypertension later in life [START_REF] Manolio | Exercise Blood Pressure Response and 5-Year Risk of Elevated Blood Pressure in a Cohort of Young Adults: The CARDIA Study[END_REF][START_REF] Miyai | Exercise BP response in subjects with high-normal BP: Exaggerated blood pressure response to exercise and risk of future hypertension in subjects with high-normal blood pressure[END_REF][START_REF] Singh | Blood Pressure Response During Treadmill Testing as a Risk Factor for New-Onset Hypertension[END_REF][START_REF] Wilson | Early prediction of hypertension using exercise blood pressure[END_REF]. Furthermore, blood pressure during exercise has been found to be more strongly related to mortality and morbidity from myocardial infarction than post exercise BP [START_REF] Mundal | Exercise Blood Pressure Predicts Mortality From Myocardial Infarction[END_REF]. Therefore, having a thorough understanding of the blood pressure response to exercise in normotensive and hypertensive individuals is of clinical significance for practitioners and those working in the health and fitness industry.

Although overweight and obese people are at an increased risk of hypertension [START_REF]Overweight and obesity[END_REF][START_REF] Hall | Pathophysiology of obesity hypertension[END_REF][START_REF] Hall | Mechanisms of obesityassociated cardiovascular and renal disease[END_REF], few studies have investigated exercise BP in this population. An increased myocardial wall thickness was found to correlate significantly with raised exercise SBP in overweight, mildly hypertensive individuals [START_REF] Pierson | Relationship between exercise systolic blood pressure and left ventricular geometry in overweight, mildly hypertensive patients[END_REF]. Elevated SBP during submaximal cycling has also been reported regardless of insulin sensitivity or cardiorespiratory fitness in individuals with a higher waist circumference [START_REF] Huot | Insulin Resistance, low cardiorespiratory fitness, and increased exercise blood pressure[END_REF]. However, while the prevalence of obesity and its associated risk factors such as hypertension has been found to be higher in men [START_REF] Hubert | Obesity as an independent risk factor for cardiovascular disease: a 26-year follow-up of participants in the Framingham Heart Study[END_REF], little is currently known on the specific pathophysiology of hypertensive overweight or obese women during exercise despite the known effects of pregnancy, menopause and contraception on hypertension [START_REF] Wenger | Hypertension Across a Woman's Life Cycle[END_REF].

The main physiological mechanisms influencing the hypertensive response during exercise in overweight and obesity could originate in autonomic system dysregulation. At the commencement of and during exercise, an exercise pressor reflex dictates that sympathetic nervous system (SNS) activity overrides parasympathetic vagal tone, and results in increased heart rate, stroke volume and cardiac output in conjunction with a simultaneous redirection of blood flow to high priority visceral organs and skeletal muscles [START_REF] Le | The Blood Pressure Response to Dynamic Exercise Testing: A Systematic Review[END_REF] to meet the increased metabolic needs of the active musculature, and drive SBP and mean arterial pressure (MAP) upward [START_REF] Myers | The physiology behind exercise testing[END_REF]. In overweight and obese people, an impaired response of SNS activity at onset of exercise may alter blood redistribution, and therefore pressure, through decreased endothelial responsiveness, increased arterial stiffness and increased hormonal response (mainly of the renin-angiotensin-aldosterone system) [START_REF] Kim | Hypertensive response to exercise: mechanisms and clinical implication[END_REF]17]. Therefore, the purpose of this study was to compare the heart rate (HR) and BP responses of normal, overweight and obese women during a graded submaximal treadmill exercise, to determine whether body composition selectively affects cardiovascular responses to exercise.

Methods

Ethics statement and participants

The procedures described in this study were granted ethical clearance by the local ethics committee on human research. Participants for this study were recruited in the local community through the use of advertisements and e-mails, and were required to provide written informed consent prior to inclusion in the study. Participants consisted of healthy, non-menopausal female individuals aged 18 to 50 years of age (n=35; age 30.8±9.5 yr; height 1.66±0.05 m; weight 73.8±18.9 kg; maximum oxygen uptake 33.5±8.1 mL•min -1 •kg -1 ) who were not smoking and not taking any medications known to affect cardiovascular measures in addition to being free from both mental and physical impairments.

Participants were invited for a preliminary visit for screening against underlying health conditions potentially affecting the study procedures and findings (Medical Health Questionnaires, lung function assessed using spirometry) and familiarisation with the procedures and equipment. Resting anthropometric characteristics of participants was recorded (height, weight, body mass index [BMI]=weight/height 2 , hip and waist circumferences, waist-to-hip ratio [W:H]) and their body composition using dual-energy xray absorptiometry (DEXA; Lunar Prodigy Advance, GE Healthcare, Buckinghamshire, UK) (total and regional body fat, muscle mass, percentage body fat, bone mineral density [BMD] and bone mineral content [BMC], and blood pressure, blood glucose and cholesterol were also measured during the initial visit.

Methodology

Each participant completed two experimental sessions separated by more than three days to prevent from potential fatigue effects between tests. Participants reported to the laboratory after a 10-12 hour overnight fast and no later than 10 AM. Hyperglycaemia was controlled using resting blood glucose, measured from a drop of blood collected at the fingertip using a single use lancet and portable analyser (Accu-Chek Advantage, Roche Diagnostics, Indianapolis, IN, USA). The first session consisted in a maximal incremental exercise test to volitional exhaustion on a treadmill (TMX425C, Trackmaster, Full Vision Inc., Newton, KS).

The rate of oxygen utilization (V ̇O2 ), was measured continuously using a two-way, non-rebreathing valve (series 2700, Hans-Rudolph, Kansas City, USA) and an automated opencircuit spirometry metabolic analysis system (True One 2400, Parvo Medics, Sandy UT).

After a two minute warm-up walking at 4 km⋅h -1 or 6 km⋅h -1 (depending on the participant's exercise history and physical characteristics), speed was increased every minute until the participant signalled they had reached a comfortable speed, whereupon the grade of the treadmill was increased by 1-2% every minute until volitional exhaustion.

The second session consisted in a submaximal test including five exercise stages, each lasting 3 min. After an initial warm-up stage at 4.5 km⋅h -1 (baseline), a graded test with four intensity stages were performed at relative intensities corresponding to 30%, 40%, 50% and 60% of V ̇O2MAX . Heart rate (HR) was measured continuously at 0.2 Hz using a chest strap (Polar Electro, Kempele, Finland). Blood pressure responses were measured twice at the end of each stage of exercise during the graded test using a manual blood pressure cuff, aneroid and stethoscope (Welch Allyn, New York USA).

Statistical analyses

Participants were classified into three groups based on BMI: normal weight (NOR; ≤24.9 kg•m 2 ), overweight (OVW; 25-29.9 kg•m 2 ) and obese (OBE; ≥30 kg•m 2 ). For comparison purposes, participants were also grouped into tertiles of percentage of body fat. Contingency tables showed strong association (p<0.001) between the two approaches and BMI groups were used for analyses.

Data are expressed as mean ± standard deviation (SD). All statistical analyses were performed using jamovi [18], and the level of significance was set at p<0.05. Differences in resting characteristics, body composition and fitness level between groups were determined using one-way ANOVAs with Bonferroni post-hoc tests. Agreement and concordance between the two measures of blood pressure taken at each level of the graded exercise were evaluated using Pearson's coefficient of correlation (r) and Kendall's rank correlation coefficient (tau-b) for SBP, DBP and MAP. The effect of exercise intensity (30%, 40%, 50% and 60%), BMI group (NOR, OVW, OBE) and their interaction (intensity×group) on HR%, SBP, DBP and MAP were assessed using 2-way, repeated measures ANCOVAs using age as a covariate of cardiovascular measures, with Bonferroni post-hoc tests. Pearson's r was used to calculate simple correlations between percentage body fat and HR%, SBP, DBP and MAP.

Effect sizes for pairwise comparisons were assessed using Cohen's d, calculated in the standard manner and interpreted according to Cohen's scale (small effect: 0.2<d<0.5, moderate effect: 0.5<d<0.8, and large effect: d>0.8). For ANOVAs and ANCOVAs, we reported effect size using partial eta-squared (η 2 p ) interpreted according to Cohen's scale (small effect: 0.01<η

Results

All participants completed the study procedures. The participant groups were homogenous in age, height, W:H ratio, DBP and resting blood glucose (Table 1). Participants in OVW and OBE group had higher weight, trunk fat and body fat (in g and %) compared to NOR (Table 1). Participants in OBE group also had higher weight, trunk fat and body fat compared to both OVW and NOR (Table 1

Discussion

The aim of this study was to determine and compare the cardiovascular responses of normal, overweight and obese women to a graded submaximal treadmill exercise. The main findings of this study were that besides anthropometric and body composition differences, i) there were no differences across groups for HR, ii) there were no significant differences in BP responses during exercise between NOR and OVW, but iii) BP responses in OBE women were significantly different to NOR at rest and to both NOR and OVW during exercise.

In the current study, HR responses can be considered normal as they increased as a function of exercise intensity, and reached maximum values within 10% of age-predicted maximum during the incremental test in all participant groups. Maximum HR values were consistent with previous literature [START_REF] Steffan | Substrate utilization during submaximal exercise in obese and normal-weight women[END_REF]. Participants also did not report adverse perceptual responses during or after exercise. We did not observe group differences in HR at the same relative exercise intensities between groups during the submaximal graded test, and age was not a significant factor of HR response. Still, despite the lack of significant differences across groups (p=0.078), visual inspection of Figure 1 indicates that HR responses to exercise appear of a lesser magnitude in the obese compared to the two other groups. Further, HR was significantly and inversely correlated with body fat only at the highest intensity (60%). Since HR is a dependent variable with a large dispersion (coefficient of variation 7-12%), the possibility of a type II error remains and warrants future research specifically aiming to measure exercise HR at higher than moderate exercise intensities.

Contrasting with normal and expected HR responses, BP characteristics differed markedly between OBE and the two other groups. Participants in OBE group were pre-hypertensive at rest [START_REF] Pescatello | ACSM's guidelines for exercise testing and prescription[END_REF] and had overall higher exercise BP than NOR and OVW, although no participant reached levels characteristic of HRE [START_REF] Kim | Hypertensive response to exercise: mechanisms and clinical implication[END_REF]. As could be expected, percentage body fat was a strong predictor of blood pressure during exercise. While overall elevated BP responses in individuals with higher fat mass are consistent with previous literature [START_REF] Huot | Insulin Resistance, low cardiorespiratory fitness, and increased exercise blood pressure[END_REF], we also observed altered BP dynamics in OBE group, with higher SBP, DBP and MAP between 30% and 50% compared to both NOR and OVW, followed by significantly lower BP responses at the highest exercise intensity (60% of V ̇O2MAX ), the highest exercise intensity currently recommended in overweight and obese individuals with underlying health conditions (diabetes, hypertension, dyslipidemia, CVD) [START_REF] Pescatello | ACSM's guidelines for exercise testing and prescription[END_REF].

Observations of unchanged HR with simultaneous exaggerated BP responses and altered BP dynamics during exercise, such as those observed specifically in the OBE group in our study, are consistent with obesity-specific SNS activity dysregulation. The main mechanism for specific SNS alterations may originate in adipose tissue inflammation in obese individuals, which has been shown to increase systemic inflammatory response and markers of oxidative stress, such as angiotensin II adipokine [START_REF] Ramalingam | The renin angiotensin system, oxidative stress and mitochondrial function in obesity and insulin resistance[END_REF]. Angiotensin is known to play a major role in the regulation of BP, as it has been shown to drive the hypertensive responses to exercise [START_REF] Shim | Exaggerated Blood Pressure Response to Exercise Is Associated With Augmented Rise of Angiotensin II During Exercise[END_REF].

Additionally, blocking angiotensin II receptors reduces SBP during exercise [START_REF] Warner | Losartan improves exercise tolerance in patients with diastolic dysfunction and a hypertensive response to exercise[END_REF]. Previous studies have also reported altered SNS activity specifically in mildly hypertensive individuals, as characterized by a reduced propensity to postexercise hypotension (the decrease in BP following dynamic exercise) [START_REF] Kenney | Postexercise hypotension. Key features, mechanisms, and clinical significance[END_REF][START_REF] Hagberg | The Role of Exercise Training in the Treatment of Hypertension[END_REF]. Therefore, together with the inconclusive observations we previously mentioned regarding HR responses to exercise, these observations provide a basis warranting future exercise studies in obese people specifically targeting responses at exercise above moderate intensities to explore SNS responses. The effect of even higher intensity exercise should also be further investigated, since high intensity interval exercise has been shown to be a time-efficient training model promoting body composition changes [START_REF] Wewege | The effects of high-intensity interval training vs. moderate-intensity continuous training on body composition in overweight and obese adults: a systematic review and meta-analysis[END_REF] and hypotensive exercise response [START_REF] Bonsu | The training and detraining effect of high-intensity interval training on post-exercise hypotension in young overweight/obese women[END_REF] comparable to the traditionally recommended moderate-intensity exercise [START_REF] Pescatello | ACSM's guidelines for exercise testing and prescription[END_REF], but the potential for SNS dysregulation occurring specifically in obese individuals has been insufficiently described.

It is important to acknowledge our findings are limited to the obese population under investigation, limited to seven, white female participants, in which we could not account for the effect of menstrual phase. However, we observed no effect of age on BP responses, no violations of the assumption of equality of variances, and the two measures of BP performed at each stage were in high agreement and concordance. In addition, although we determined participant groups based on BMI, which is known to be inaccurately representing body composition, results were unchanged when using tertiles of percentage body fat. For increased practical applicability, we used BMI classification for all analyses. Finally, for practical reasons we did not measure SNS activity directly or indirectly, and we did not measure postexercise BP. These limitations should be taken in consideration before extrapolating our results to a wider population or derive conclusive evidence on the role of adipokines and SNS activity from our discussion.

Perspectives

Our study further contributes to underscore the increased risks apparently healthy obese women are placed at to developing diseases from the chronic exposure to raised BP despite Speed (km⋅h -1 ) 30% 4.6 ± 1.0 4.0 ± 0.8 2.0 ± 0.5 40% 5.6 ± 0.9 5.1 ± 0.8 3.7 ± 1.0 50% 6.6 ± 1.0 6.1 ± 0.9 4.9 ± 0.7 60% 7.5 ± 1.2 6.0 ± 0.7 5.7 ± 0.6 Gradient (%) 30% 0.5 ± 0 0.5 ± 0 0.5 ± 0 40% 0.5 ± 0 0.5 ± 0 0.5 ± 0 50% 0.7 ± 0.5 0.5 ± 0 0.5 ± 0 60%

1.1 ± 1.4 1.0 ± 0.9 0.5 ± 0 Data are mean ± SD

Figure Figure 1 .

 1 Figure

  ). Participants in OBE group had greater LBM, and resting SBP and MAP compared to NOR only (Table1). At rest, all but one participant in OBE group Absolute speed and gradient achieved at each stage of the submaximal graded test are presented in Table2. Results for HR% are presented in Figure1. There was a significant and The two measures of SBP, DBP and MAP performed at each exercise intensity were in high agreement and concordance (Table3). No participant achieved SBP characteristic of HRE

	revealed SBP in OBE group was significantly different from NOR (p=0.015) and OVW
	(p=0.002), with no significant differences between NOR and OVW (p=0.958).
	large main effect of exercise intensity on HR% (p<0.001; η 2 For DBP, there was no significant effect of intensity (p=0.912; η 2 p =0.473), with no significant p =0.006) but a significant
	differences across groups (p=0.078; η 2 and large main effect of group (p<0.001; η 2 p =0.152) and no significant interaction between group p =0.416), with no significant effect of interaction
	and exercise intensity (p=0.232; η 2 (p=0.219; η 2 p =0.089). There was no significant effect of age (p=0.792; η 2 p =0.082). There was no significant effect of age as a p =0.002). Post-hoc
	covariate of HR% (p=0.326; η 2 testing revealed DBP in OBE group was significantly different from NOR (p=0.004) and p =0.031).
	*** Insert Table 2 about here *** OVW (p<0.001), with no significant differences between NOR and OVW (p=1.000).
	*** Insert Figure 1 about here *** For MAP, there were significant and large main effects of exercise intensity (p<0.001;
	η 2	p =0.232) and group (p<0.001; η 2	p =0.430), with no main effect of interaction (p=0.160;
	η 2	p =0.099). There was no significant effect of age (p=0.812; η 2	p =0.002). Post-hoc testing
	revealed DBP in OBE group was significantly different from NOR (p=0.004) and OVW
	(p<0.001), with no significant differences between NOR and OVW (p=0.977).
	Percentage body fat was significantly inversely correlated with HR% only at 60% (r=-0.464,
	p=0.006), with SBP at all intensity levels (30%: r=0.500, p=0.004 ; 40%: r=0.448, p=0.012 ;
	50%: r=0.471, p=0.008 ; 60%: r=0.522, p=0.003), with DBP at all intensity levels (30%:
	r=0.634 ; 40%: r=0.644 ; 50%: r=0.695, 60%: r=0.682 ; all correlations p<0.001), and with
	MAP at all intensity levels (30%: p=0.594, p<0.001 ; 40%: r=0.585, p<0.001 ; 50%: r=0.630
	MAP: 103±12 mmHg) and OVW (SBP: 141±15 mmHg; DBP: 86±9 mmHg; MAP: 104±11 ; 60%: r=0.649 ; all correlations p<0.001).
	mmHg) compared to 50% in OBE (SBP: 148±17 mmHg; DBP: 95±10 mmHg; MAP: 112±11
	mmHg).
	were pre-hypertensive, and one participant of OVW group was hypertensive (147/100
		*** Insert Table 3 about here ***
	mmHg).
	*** Insert Table 1 about here *** For SBP, there were significant and large main effects of exercise intensity (p<0.001;
	η 2	p =0.389) and group (p=0.001; η 2	p =0.370), with no main effect of interaction (p=0.570;
	η 2	p =0.052). There was no significant effect of age (p=0.894; η 2	p =0.001). Post-hoc testing

(>190 mmHg), and all participants with resting pre-hypertension and hypertension had normal exercise BP (maximum 172/80 mmHg). The dynamics of BP response were markedly different between OBE and the two other groups (Figure

1

): minimum BP responses were observed at 30% in NOR (SBP: 116±15 mmHg; DBP: 81±5 mmHg; MAP: 93±8 mmHg) and OVW groups (SBP: 112±11 mmHg; DBP: 79±6 mmHg; MAP: 90±6 mmHg) compared to 60% in OBE (SBP: 134±13 mmHg; DBP: 82±6 mmHg; MAP: 100±7 mmHg), and maximum BP responses were observed at 60% in NOR (SBP: 141±19 mmHg; DBP: 84±10 mmHg;

Table 1 .

 1 Participants' resting anthropometry and blood pressure profiles classified according to BMI.

	Tables
		Normal	Overweight	Obese	ANOVA
		<24.9 kg•m 2	25-29.9 kg•m 2	>30 kg•m 2	p	η 2 p
		(n = 15)	(n = 13)	(n = 7)
	Weight (kg)	60.9 ± 7.8	72.3 ± 3.5 A C	104.4 ± 18.4 B	<0.001	0.751
	Height (m)	1.65 ± 0.05	1.65 ± 0.05	1.68 ± 0.06	0.484	0.044
	Age (yr)	28.3 ± 10.1	33.4 ± 8.9	31.6 ± 8.8	0.362	0.062
	W:H ratio	0.74 ± 0.04	0.77 ± 0.05	0.78 ± 0.04	0.065	0.166
	Trunk fat (kg)	5.0 ± 2.5	8.1 ± 2.2 A C	18.7 ± 5.2 B	<0.001	0.760
	Body fat (kg)	17.6 ± 5.7	25.6 ± 4.0 A C	51.6 ± 10.2 B	<0.001	0.798
	Body fat (%)	30.0 ± 7.0	36.8 ± 5.3 A C	51.2 ± 2.5 B	<0.001	0.660
	LBM (kg)	40.2 ± 4.3	43.9 ± 4.2	49.1 ± 8.5 A	0.020	0.230
	HR max (%)	188 ± 9	184 ± 7	186 ± 7	0.451	0.049
	SBP (mmHg)	110 ± 11	117 ± 12	132 ± 18 B	0.003	0.327
	DBP (mmHg)	70 ± 9	74 ± 10	79 ± 10	0.164	0.114
	MAP (mmHg)	84 ± 9	88 ± 10	96 ± 11 A	0.027	0.214
	Glucose (mmol•L -1 )	5.2 ± 0.5	5.3 ± 0.4	5.5 ± 0.4	0.348	0.064
	Data are mean ± SD
	A p < 0.05 from BMI <24.9 kg•m 2
	B p < 0.001 from BMI <24.9 kg•m 2

C p < 0.001 from BMI >30 kg•m 2 Abbreviations used: W:H (waist-to-hip); LBM (lean body mass); SBP (systolic blood pressure); DBP (diastolic blood pressure).

Table 2 .

 2 Speed, gradient and heart rate (% of maximum) achieved at each stage of the graded test and classified according to BMI.

	Normal	Overweight	Obese
	<24.9 kg•m 2	25-29.9 kg•m 2	>30 kg•m 2
	(n = 15)	(n = 13)	(n = 7)

Table 3 .

 3 Indicators of agreement and concordance between measures of blood pressure during the graded test.

		SBP	DBP	MAP
	Baseline
	Pearson' r	0.936 A	0.889 A	0.935 A
	Kendall's tau-b	0.762 A	0.739 A	0.766 A
	30% VO2MAX
	Pearson' r	0.821 A	0.838 A	0.868 A
	Kendall's tau-b	0.627 A	0.778 A	0.672 A
	40% VO2MAX
	Pearson' r	0.886 A	0.833 A	0.905 A
	Kendall's tau-b	0.729 A	0.707 A	0.697 A
	50% VO2MAX
	Pearson' r	0.933 A	0.892 A	0.931 A
	Kendall's tau-b	0.766 A	0.715 A	0.707 A
	60% VO2MAX
	Pearson' r	0.931 A	0.891 A	0.945 A
	Kendall's tau-b	0.782 A	0.732 A	0.809 A
	A p < 0.001
	Abbreviations used: SBP (systolic blood pressure); DBP (diastolic blood pressure);
	MAP (mean arterial pressure).

approval project S/11/317, University of the Sunshine Coast

Symbols * and † denote significant main effects (p<0.01) of exercise intensity and group, respectively.