Se ´bastien Boyas
email: sebastien.boyas@uottawa.ca

Anthony Remaud

Etienne J Bisson

Se ´bastien Cadieux

Baptiste Morel

Martin Bilodeau

Impairment in postural control is greater when ankle plantarflexors and dorsiflexors are fatigued simultaneously than when fatigued separately

Keywords:

Introduction

Postural control or balance is a prerequisite for completing activities of daily living and for the optimal performance of physical activities [START_REF] Murphy | Risk factors for lower extremity injury: a review of the literature[END_REF]. Postural control requires the dynamic integration and constant re-weighting of information from visual, vestibular and somatosensory systems, which control the continuous muscular corrections needed to maintain the body center of mass (COM) within the base of support [START_REF] Johansson | Human postural dynamics[END_REF]. In this context, the projection of the COM falls anterior to the axis of the talocrural joint, and consequently, calf muscles are considered to play a major role in postural control [START_REF] Panzer | Biomechanical assessment of quiet standing and changes associated with aging[END_REF]. Indeed, it has been reported that the ankle musculature, i.e. plantarflexors (PFs) and dorsiflexors (DFs), plays a central role in maintaining balance during single and bilateral limb stances [START_REF] Riemann | Comparison of the ankle, knee, hip, and trunk corrective action shown during single-leg stance on firm, foam, and multiaxial surfaces[END_REF]. Moreover, several studies concluded that both gastrocnemii and soleus muscles play a significant role in postural corrections, mainly in the antero-posterior plane [START_REF] Schieppati | Group II spindle afferent fibers in humans: their possible role in the reflex control of stance[END_REF]. On the other hand, Di Giulio et al. [START_REF] Giulio | The proprioceptive and agonist roles of gastrocnemius, soleus and tibialis anterior muscles in maintaining human upright posture[END_REF] suggested that the tibialis anterior muscle is a better source of proprioceptive information than the active agonists (soleus and gastrocnemius).

Muscle fatigue is a complex phenomenon involving numerous sites of the neuromuscular system [START_REF] Boyas | Neuromuscular fatigue in healthy muscle: underlying factors and adaptation mechanisms[END_REF]. Fatigue has been reported to have adverse effects on movement-related variables, including impairments in muscle contractile efficiency [START_REF] Ament | Exercise and fatigue[END_REF] and decreased proprioception [START_REF] Forestier | Alteration of the position sense at the ankle induced by muscular fatigue in humans[END_REF]. Fatigue also affects more complex functions such as tasks involving manipulation (e.g. [START_REF] Bisson | Hand steadiness of older adults fail to recover 20 minutes after fatigue[END_REF]), stopping/jumping (e.g. [START_REF] Chappell | Effect of fatigue on knee kinetics and kinematics in stop-jump tasks[END_REF]), reaching (e.g. [START_REF] Fuller | Posture-movement changes following repetitive motion-induced shoulder muscle fatigue[END_REF]), and of particular interest for the present study, tasks requiring the maintenance of an upright posture (e.g. [START_REF] Bisson | Acute effects of fatigue of the plantarflexor muscles on different postural tasks[END_REF]).

Recently, numerous studies focused on the effects of ankle muscle fatigue on postural control during standing [START_REF] Bisson | Acute effects of fatigue of the plantarflexor muscles on different postural tasks[END_REF][START_REF] Adlerton | Does calf-muscle fatigue affect standing balance?[END_REF][START_REF] Corbeil | Perturbation of the postural control system induced by muscular fatigue[END_REF][START_REF] Dickin | Postural stability in altered and unaltered sensory environments following fatiguing exercise of lower extremity joints[END_REF][START_REF] Gribble | Effect of hip and ankle muscle fatigue on unipedal postural control[END_REF][START_REF] Gribble | Effect of lower-extremity muscle fatigue on postural control[END_REF][START_REF] Harkins | Effects of 2 ankle fatigue models on the duration of postural stability dysfunction[END_REF][START_REF] Ledin | Effects of postural disturbances with fatigued triceps surae muscles or with 20% additional body weight[END_REF][START_REF] Lundin | Effect of plantar flexor and dorsiflexor fatigue on unilateral postural control[END_REF][START_REF] Nardone | Time course of stabilometric changes after a strenuous treadmill exercise[END_REF][START_REF] Reimer 3rd | Functional fatigue of the hip and ankle musculature cause similar alterations in single leg stance postural control[END_REF][START_REF] Vuillerme | Attentional demands and postural sway: the effect of the calf muscles fatigue[END_REF][START_REF] Yaggie | Effects of isokinetic ankle fatigue on the maintenance of balance and postural limits[END_REF]. Although a significant effect of muscle fatigue on posture appears predominant, results are inconsistent which may be due to methodological differences across studies (i.e. fatigue protocols,

A B S T R A C T

The aim of the present study was to compare the effects of ankle muscle fatigue on postural control when plantarflexors (PFs) and dorsiflexors (DFs) are fatigued simultaneously compared with separately. This study also investigated the recovery of postural control after fatigue. Sixteen adults (eight women and eight men) performed postural trials before and after an isokinetic fatigue task involving either (i) only PFs (308 s À1 ), (ii) only DFs (1208 s À1 ), or (iii) both PFs and DFs simultaneously. The fatigue task involved maximal contractions repeated until the torque produced decreased below 50% of the maximal torque. Postural trials lasted 30 s and were performed on one leg with eyes open (EO) or eyes closed (EC). Sway area, medio-lateral (ML) and antero-posterior (AP) positions and velocities were calculated from the center of pressure displacements. With EO, no effect of fatigue was found on postural variables. With EC, sway area and AP velocity increased only when both PFs and DFs were fatigued simultaneously. An effect of fatigue present only when both muscle groups are fatigued simultaneously could be due to impairment in the compensatory activity between agonist and antagonist muscles and/or a greater decrease in proprioception due to a greater number of fatigued muscles. In addition, when PFs and DFs were fatigued simultaneously, sway area and AP velocity returned to pre-fatigue values within 2 min, whereas a posterior shift in AP position persisted for 10 min. This last result may suggest a longer-lasting change in postural strategy needed for optimal postural control.

ß 2011 Elsevier B.V. All rights reserved.

postural stance used, visual information available). Indeed, whereas some studies report no changes in postural control after fatigue of ankle PFs [START_REF] Adlerton | Does calf-muscle fatigue affect standing balance?[END_REF][START_REF] Gribble | Effect of hip and ankle muscle fatigue on unipedal postural control[END_REF], most investigations conclude that ankle muscle fatigue negatively affects postural control. This has been shown with and without vision and regardless of the postural task tested (one-or two-leg stance) after isolated fatigue of the ankle PFs [START_REF] Bisson | Acute effects of fatigue of the plantarflexor muscles on different postural tasks[END_REF][START_REF] Corbeil | Perturbation of the postural control system induced by muscular fatigue[END_REF][START_REF] Ledin | Effects of postural disturbances with fatigued triceps surae muscles or with 20% additional body weight[END_REF][START_REF] Vuillerme | Attentional demands and postural sway: the effect of the calf muscles fatigue[END_REF], or after simultaneous fatigue of ankle PFs and DFs [START_REF] Dickin | Postural stability in altered and unaltered sensory environments following fatiguing exercise of lower extremity joints[END_REF][START_REF] Gribble | Effect of lower-extremity muscle fatigue on postural control[END_REF][START_REF] Harkins | Effects of 2 ankle fatigue models on the duration of postural stability dysfunction[END_REF][START_REF] Lundin | Effect of plantar flexor and dorsiflexor fatigue on unilateral postural control[END_REF][START_REF] Nardone | Time course of stabilometric changes after a strenuous treadmill exercise[END_REF][START_REF] Reimer 3rd | Functional fatigue of the hip and ankle musculature cause similar alterations in single leg stance postural control[END_REF][START_REF] Yaggie | Effects of isokinetic ankle fatigue on the maintenance of balance and postural limits[END_REF]. However, a direct comparison of the effect of fatigue of these two muscle groups has not been carried out. Therefore, the main purpose of this study was to compare the effects of ankle muscle fatigue on postural sway when PFs and DFs are fatigued simultaneously compared with separately. We hypothesized that postural sway would increase more when both muscle groups are fatigued simultaneously compared with separately. This hypothesis stems from the assumption that the neuromuscular system may be able to compensate for the fatigue-related decrease in postural control more readily if at least one non-fatigued muscle group can optimally provide proprioceptive information or generate appropriate actions.

A secondary purpose was to investigate the recovery of postural control after impairment induced by ankle muscle fatigue. Postfatigue recovery of sway features has been poorly documented in literature, with different conclusions. Some studies indicate that the effects of simultaneous fatigue of ankle PFs and DFs on postural control during unipedal stance with eyes open can persist at least 10 min [START_REF] Dickin | Postural stability in altered and unaltered sensory environments following fatiguing exercise of lower extremity joints[END_REF][START_REF] Gribble | Effect of lower-extremity muscle fatigue on postural control[END_REF][START_REF] Harkins | Effects of 2 ankle fatigue models on the duration of postural stability dysfunction[END_REF][START_REF] Lundin | Effect of plantar flexor and dorsiflexor fatigue on unilateral postural control[END_REF][START_REF] Nardone | Time course of stabilometric changes after a strenuous treadmill exercise[END_REF][START_REF] Reimer 3rd | Functional fatigue of the hip and ankle musculature cause similar alterations in single leg stance postural control[END_REF][START_REF] Yaggie | Effects of isokinetic ankle fatigue on the maintenance of balance and postural limits[END_REF]. On the other hand, Harkins et al. [START_REF] Harkins | Effects of 2 ankle fatigue models on the duration of postural stability dysfunction[END_REF] indicated that postural control during unipedal stance with eyes closed recovered very quickly (less than a minute) after isokinetic fatigue of the same muscles. These variable results may be explained by discrepancies in experimental designs such as the duration of the fatigue protocol and the muscles fatigued. It was expected that the effects of fatigue on postural control would recover quickly as the experimental conditions of the present study are close to those of Harkins et al. [START_REF] Harkins | Effects of 2 ankle fatigue models on the duration of postural stability dysfunction[END_REF].

Methods

Subjects

Sixteen (eight women and eight men) healthy adults (21.9 AE 3.5 years, 174.3 AE 8.3 cm, 69.4 AE 9.3 kg) volunteered for the present study. Subjects were clearly informed of the purpose of the study before their written consent was obtained. The research protocol was approved by the research ethics boards of the E ´lisabeth Bruye `re Research Institute and of the University of Ottawa. None of the subjects presented with any history of injury, surgery or pathology of the lower limb that could affect their ability to perform the experiment.

Apparatus

A force platform (AMTI Acu-Gait 1 , AMTI 1 , Watertown, USA) was used to measure the displacements of the center of pressure (COP) during postural trials (sampling frequency: 50 Hz). An isokinetic dynamometer (Biodex System 3 Pro 1 , Biodex Medical Systems, Shirley, USA) was used to assess the maximal voluntary isokinetic torque (MVT) of ankle PFs and DFs and to perform fatigue protocols.

Experimental procedure

Subjects participated in three experimental sessions (Fig. 1) performed approximately one week apart. Sessions were identical except for the muscle group(s) fatigued: ankle PFs only, ankle DFs only, both PFs and DFs simultaneously (PFs + DFs). The order of experimental sessions was counterbalanced across subjects. During postural trials, subjects had to stand barefoot on their right leg under two vision conditions: with eyes open (EO) and with eyes closed (EC). All postural trials lasted 30 s. Subjects were instructed to sway as little as possible while standing. During these postural trials, subjects started with their arms along their body and were able to use their arms to maintain their balance. For trials performed with EO, subjects were instructed to look at a mark placed on the wall 2.5 m in front of them. For trials performed with EC, subjects were instructed to lift their left leg, find their balance, and then close their eyes.

After familiarization to the postural task, subjects sat on the dynamometer so that the hip was flexed at 708 (08 = full extension), and the knee fully extended. After a brief warm-up, subjects performed three maximal isokinetic contractions of ankle PFs (308 s À1 ) and/or ankle DFs (1208 s À1 ) according to the experimental session. This allowed the dynamic assessment of the MVT for each velocity. Then, subjects performed eight pre-fatigue (PRE) postural trials (four for each vision condition). Afterwards, subjects performed one of the three fatigue protocols, which consisted of maximal isokinetic contractions of (i) only PFs (308 s À1 ); (ii) only DFs (1208 s À1 ); or (iii) both PFs (308 s À1 ) and DFs (1208 s À1 ), repeated until the torque produced decreased below 50% MVT for three consecutive contractions. Different velocities were chosen for isokinetic contractions of PFs and DFs muscles in order to reach similar time to fatigue for both muscle groups as done previously [START_REF] Harkins | Effects of 2 ankle fatigue models on the duration of postural stability dysfunction[END_REF][START_REF] Bisson | Effects of ankle and hip muscle fatigue on postural sway and attentional demands during unipedal stance[END_REF][START_REF] Ochsendorf | Effect of orthotics on postural sway after fatigue of the plantar flexors and dorsiflexors[END_REF]. Subjects were given strong verbal encouragements during maximal contractions and all fatigue tests. Immediately after the fatigue protocol (15-20 s), subjects performed two post-fatigue (POST) postural trials, one with EO, and one with EC (order counterbalanced). Within each experimental session, the fatigue protocol and two POST trials were performed four times (Fig. 1) for a total of eight POST postural trials (four for each vision condition). The fatigue protocol was repeated after every two POST postural trials to minimize the potential rapid recovery of sway on POST data. Finally, after the last two POST trials, subjects alternated 1 min of recovery seated on a chair and two recovery (REC) postural trials (one for each vision condition), to record a total of 16 REC postural trials (eight for each vision condition). For each postural trial, subjects placed their foot at the same location on the force platform by matching a template footprint drawn on the platform.

Data analysis

COP data were used to calculate five postural variables: the area of the 95% confidence ellipse (sway area, cm 2 ), the mean COP position and the mean sway velocity in the medio-lateral (ML position, cm; ML velocity, cm s À1 ) and antero-posterior (AP position, cm; AP velocity, cm s À1 ) directions. These variables are frequently assessed in postural control studies and have good validity and reliability [START_REF] Ruhe | The test-retest reliability of centre of pressure measures in bipedal static task conditions-a systematic review of the literature[END_REF]. During a postural trial, when a step occurred, the trial was removed from data analysis. This represented 5% of the total number of trials (i.e. 75 trials out of a total of 1536 trials). However, statistical analyses including postural trials where subjects took a step led to similar results as those presented hereafter.

[ ( F i g . _ 1 ) T D $ F I G ] E O E C E C E O E C E C E O E C E C E O E C E C F4 F1 F3 F2 E C E O E C E C E O E C E C E O E C E C E O E C Counterbalanced Pre-fatigue trials Post-fatigue trials Recovery trials R R R R R R R R E O E O E O E O E O E O E O E O

Statistical analysis

First, two-way analyses of variance (ANOVA) for repeated measures were used to assess the effects of the muscle group involved during the fatigue tests (PFs + DFs, DFs, PFs) and the effects of the fatigue test number (test 1, test 2, test 3, test 4) on the duration and on the number of contractions of the fatigue tests. Second, threeway ANOVAs for repeated measures were used to assess the effects of vision (EO, EC), fatigue (PRE, POST), and muscle group (PFs + DFs, DFs, PFs) on the five postural variables (sway area, ML and AP positions, ML and AP velocities). Third, two-way ANOVAs for repeated measures were used to assess the effects of fatigue (PRE, POST) and muscle group (PFs + DFs, DFs, PFs) on the five postural variables, considering postural trials performed with EC and EO separately. Fourth, considering the results of the task with the greatest fatigue-related changes in postural control (i.e. PFs + DFs with EC), one-way ANOVAs for repeated measures were used to assess the effect of fatigue and recovery (PRE, POST, REC1 to REC8) on the postural variables. For all statistical tests, the significance level was set at 0.05. When relevant, post hoc tests were performed by means of Newman-Keuls procedures. When the sphericity assumption in repeated measures ANOVAs was violated (Mauchly's test), a Geisser/Greenhouse correction was used.

Results

Fatigue tests characteristics

The two-way ANOVAs (muscle group  test number) revealed a main effect of the muscle group for the duration and the number of contractions of the fatigue tests. The duration of the fatigue test was significantly (p < 0.05) longer for the PFs + DFs session (92.9 AE 52.9 s) than for PFs sessions (58.9 AE 28.9 s). There was no difference between DFs sessions (71.0 AE 47.6 s) and PFs + DFs or PFs sessions (Table 1). The number of contractions performed during the DFs sessions (77 AE 43) was significantly (p < 0.05) higher than the one of the PFs sessions (38 AE 15). There was no difference between PFs + DFs (55 AE 42) and DFs or PFs sessions (Table 1).

Influence of the muscle group fatigued on postural control with eyes open or eyes closed

Main effect of vision

The three-way ANOVAs (vision  fatigue  muscle group) revealed a main effect of vision for sway area, ML velocity, and AP velocity (Table 2). Mean values of these postural variables were significantly (p < 0.001) higher for postural trials performed with EC than with EO.

Main effect of fatigue

The three-way ANOVAs (vision  fatigue  muscle group) revealed a main effect of fatigue for sway area, AP velocity, and AP position (Table 2). Mean values of sway area and AP velocity were significantly (p < 0.01) higher for POST postural trials than PRE trials. The AP position significantly (p < 0.01) shifted backward after fatigue.

Interaction of vision by fatigue

The three-way ANOVAs (vision  fatigue  muscle group) revealed an interaction between fatigue and vision for sway area, and AP velocity (Table 2). With EO, sway area POST was 7% higher than PRE (9.8 AE 3.3 cm 2 vs. 9.2 AE 2.7 cm 2 , p < 0.01). With EC, sway area POST was 14% higher than PRE (24.2 AE 6.1 cm 2 vs. 21.3 AE 5.0 cm 2 , p < 0.001). With EO, AP velocity POST was 6% higher than PRE (2.2 AE 0.5 cm s À1 vs. 2.1 AE 0.5 cm s À1 , p = 0.003). With EC, AP velocity POST was 9% higher than PRE (4.4 AE 1.0 cm s À1 vs. 4.0 AE 1.0 cm s À1 , p < 0.001).

Interaction of vision by muscle group

The three-way ANOVAs (vision  fatigue  muscle group) revealed an interaction between muscle group and vision for sway area. With EO, there was no significant difference in sway area between the three experimental sessions (p > 0.05). With EC, sway area during the PFs + DFs session (24.4 AE 4.7 cm 2 ) was 13% and 11% higher than the sway area recorded during DFs (21.7 AE 5.1 cm 2 , p = 0.008), and PFs (22.0 AE 6.9 cm 2 , p = 0.004) sessions, respectively (Fig. 2). These last two interactions (vision  fatigue and vision  musmuscle group) suggested that the effects of fatigue and/or differences across the three sessions depended on the vision condition. Thus, further statistical analyses were performed separating postural trials performed with EC vs. EO.

3.3.

Fatigue  muscle group analyses (trials performed with EC and EO are separated)

Postural trials performed with EO

The two-way ANOVAs (fatigue  muscle group) revealed neither main effects nor interactions for the five postural variables.

Postural trials performed with EC

Sway area.

A main effect of fatigue (F = 39.4, p < 0.001) and a fatigue  muscle group interaction (F = 4.4, p < 0.02) were found significant for sway area. Sway area POST was not different from PRE for PFs and DFs sessions (p > 0.05), whereas it was 25% higher for the PFs + DFs session (27.1 AE 4.3 cm 2 vs. 21.8 AE 3.5 cm 2 , p < 0.001, Fig. 3A).

AP and ML velocity.

A main effect of fatigue (F = 24.8, p < 0.001) and a fatigue  muscle group interaction (F = 3.8, p < 0.03) were found significant for AP velocity, whereas neither main effects nor interactions were found for ML velocity. AP velocity POST was not different from PRE for PFs and DFs sessions (p > 0.05), whereas it was 17% higher than PRE for the PFs + DFs session (4.7 AE 1.0 cm s À1 vs. 4.0 AE 1.0 cm s À1 , p < 0.001, Fig. 3B).

AP and ML position.

A main effect of fatigue (F = 70.7, p < 0.001) was found for AP position whereas neither main effects nor interactions were observed for ML position. AP position moved posteriorly by about 1 cm from PRE to POST (0.0 AE 1.4 cm vs. À1.1 AE 1.5 cm, p < 0.001).

Recovery

One-way ANOVAs revealed a main effect of time for sway area (F = 7.4, p < 0.001), AP velocity (F = 12.4, p < 0.001), and AP position (F = 13.5, p < 0.001). For sway area (Fig. 4A) and AP velocity (Fig. 4B), POST values were higher than PRE (p < 0.001), whereas all recovery values (R1-R8) were not different from PRE (p > 0.05). For AP position (Fig. 4C), the POST and first six recovery values were different from PRE (p < 0.001).

Discussion

The aim of the present study was to compare the effects of ankle muscle fatigue on postural sway during quiet unipedal standing, with and without vision, when PFs and DFs were fatigued simultaneously or separately. Our main results revealed that postural control is impaired to a greater extent when ankle PFs and DFs are fatigued simultaneously compared with separately, but only when visual information is removed. We also observed that sway area and AP velocity returned to baseline within 2 min, whereas AP position remained altered for 10 min.

Effects of vision and fatigue

As found by others [START_REF] Bisson | Acute effects of fatigue of the plantarflexor muscles on different postural tasks[END_REF][START_REF] Corbeil | Perturbation of the postural control system induced by muscular fatigue[END_REF][START_REF] Ledin | Effects of postural disturbances with fatigued triceps surae muscles or with 20% additional body weight[END_REF], postural sway area and AP velocity increased when vision was removed, which indicates the importance of visual information for postural stability. Our results also revealed that fatigue of the ankle musculature, regardless of the fatigued muscle groups, altered postural sway and AP velocity, which was expected and in accordance with literature (e.g. [START_REF] Dickin | Postural stability in altered and unaltered sensory environments following fatiguing exercise of lower extremity joints[END_REF][START_REF] Gribble | Effect of lower-extremity muscle fatigue on postural control[END_REF][START_REF] Harkins | Effects of 2 ankle fatigue models on the duration of postural stability dysfunction[END_REF]). The impairment of postural control after fatigue may be related to alterations in both sensory and motor processes, such as impaired proprioception [START_REF] Vuillerme | Tongue-placed tactile biofeedback suppresses the deleterious effects of muscle fatigue on joint position sense at the ankle[END_REF], and an altered ability to produce [ ( F i g . _ 2 ) T D $ F I G ] force [START_REF] Vuillerme | Muscle fatigue degrades force sense at the ankle joint[END_REF]. These alterations could lead to inappropriate or delayed stabilizing muscle activation, leading to a decrement in postural control [START_REF] Lephart | Proprioception of the ankle and knee[END_REF].

[ ( F i g . _ 3 ) T D $ F I G ]
More precisely, the interaction between vision and fatigue revealed that after the fatigue protocol, sway area and AP velocity increased by 7% and 6% respectively with EO, whereas increases were 14% and 9% with EC. Thus, the fatigue effect on postural control appears greater with no vision. These results are in accordance with previous studies [START_REF] Bisson | Acute effects of fatigue of the plantarflexor muscles on different postural tasks[END_REF][START_REF] Vuillerme | Can vision compensate for a lower limbs muscular fatigue for controlling posture in humans?[END_REF] and suggest that vision can compensate for the impaired postural control due to muscle fatigue. The compensatory role of vision in the maintenance of postural control was further supported by the results of the twoway ANOVAs (fatigue  muscle group) performed on the data from postural trials performed with EO, where no effect of fatigue was found regardless of the muscle group(s) fatigued [START_REF] Adlerton | Does calf-muscle fatigue affect standing balance?[END_REF][START_REF] Gribble | Effect of hip and ankle muscle fatigue on unipedal postural control[END_REF].

We observed no effect of fatigue for ML velocity and ML position. This is in accordance with another study reporting an effect of fatigue in the AP but not the ML direction after ankle PFs and DFs fatigue [START_REF] Gribble | Effect of lower-extremity muscle fatigue on postural control[END_REF]. This can appear surprising, as muscles producing inversion and eversion also take part in plantarflexion and dorsiflexion. For example, the extensor hallucis longus contributes to dorsiflexion and inversion, and the peroneus longus to plantarflexion and eversion. Possibly, muscles primarily involved in the control of COP sway in the ML direction (ankle invertors and evertors) were not fatigued enough (because they were not prime movers) by our fatigue protocol to induce a significant impairment in ML velocity and position.

Effect of the muscle group fatigued

Considering the characteristics of the fatigue tests, one may have expected greater fatigue effects for the PFs + DFs session because it was associated with longer durations. However, considering the facts that: (1) the criterion to end the fatigue task was the same in the three sessions, (2) the duration of the tasks was not different between the PFs + DFs and DFs sessions, and (3) the number of contractions was higher in the DFs compared with PFs + DFs session; we believe that the differences in the fatigue effects between the three sessions were mainly due to the muscle group(s) fatigued (PFs only, DFs only, and PFs + DFs).

As mentioned above, there was no effect of fatigue for any of the sessions (PFs + DFs, PFs, DFs) when considering the EO condition. When considering data from the EC condition, our results revealed that sway area and AP velocity collected after the fatigue of only one muscle group were not significantly different from those collected before fatigue (Fig. 3). In contrast, these two variables were respectively 25% and 17% higher than PRE when both muscle groups were fatigued simultaneously. To our knowledge, our study is the first to compare the effects on postural control of fatiguing ankle PFs and DFs separately or simultaneously. Our results suggest that postural control is impaired to a greater extent when both muscle groups are fatigued simultaneously compared with separately which confirms our hypothesis. We offer two explanations for this result. First, the neuromuscular system may be able to more readily compensate for the impaired postural control following fatigue of a single muscle group relying on the antagonist muscle group, whereas this would be not possible (or to a lesser extent) if both muscle groups are fatigued. Such compensatory activity between synergist muscles after specific fatigue of one or several muscles has been reported before [START_REF] Aymard | Changes in reciprocal and transjoint inhibition induced by muscle fatigue in man[END_REF][START_REF] Duchateau | Behaviour of short and long latency reflexes in fatigued human muscles[END_REF]. These authors have suggested that fatigue of one synergist muscle can induce changes in the supraspinal activity regulating the activity of the other muscle(s). Secondly, one can assume that with more muscles fatigued, the proprioception impairment associated with fatigue could be more important and consequently lead to a greater decrease in postural control.

Recovery of postural variables

The other aim of the present study was to document the duration of the transient effect of ankle muscle fatigue on postural control. To address this objective, we only considered the experimental session that induced the greatest fatigue effects, i.e. the PFs + DFs session.

Results indicated that sway area and AP velocity were altered by the PFs + DFs fatigue protocol and returned to pre-fatigue values within 2 min (Fig. 4). These results are similar to those of Harkins et al. [START_REF] Harkins | Effects of 2 ankle fatigue models on the duration of postural stability dysfunction[END_REF] who reported that sway velocity was impaired for approximately 35 s after the same fatigue protocol. On the other hand, our results are different from those of others who report that fatigue effects persist at least 10 min [START_REF] Nardone | Time course of stabilometric changes after a strenuous treadmill exercise[END_REF][START_REF] Yaggie | Effects of isokinetic ankle fatigue on the maintenance of balance and postural limits[END_REF]. These differences could be explained by the discrepancies in implemented fatigue protocols. Indeed, fatigue in these later studies was of either long duration (i.e. 25 min [START_REF] Nardone | Time course of stabilometric changes after a strenuous treadmill exercise[END_REF]), or involved muscle groups acting in both sagittal and frontal planes [START_REF] Yaggie | Effects of isokinetic ankle fatigue on the maintenance of balance and postural limits[END_REF]. In our protocol, the mediallateral stabilizers of the ankle joint were not fatigued, and may have compensated for anterior-posterior stabilizers fatigue [START_REF] Harkins | Effects of 2 ankle fatigue models on the duration of postural stability dysfunction[END_REF]. The short duration of the effect of muscle fatigue on postural control could thus be due to the nature of the fatigue protocol (maximal isokinetic concentric contractions) that induced mainly peripheral fatigue that is restored quickly. For example, it has been reported that force was restored within 2 min after isometric contractions sustained until force declined below 50% MVC [START_REF] Sahlin | Relationship of contraction capacity to metabolic changes during recovery from a fatiguing contraction[END_REF].

Our results indicated that changes in AP position due to fatigue persisted longer (more than 10 min) than for the other variables. More specifically, fatigue induced a posterior shift of the COP. In contrast, Vuillerme et al. [START_REF] Vuillerme | Attentional demands and postural sway: the effect of the calf muscles fatigue[END_REF] reported that the COP position shifted forward after fatigue of ankle PFs, but for a bilateral stance task. Thus, the shift in COP position, which may suggest a longerlasting change in the strategy needed for optimal postural control, appears to be task-specific. One possible explanation for a posterior shift in the mean position of the COP is that subjects may have changed their overall posture after fatigue. With ankle muscles fatigued, particularly the PFs which are important contributors to postural corrections, a posterior shift of the COP effected through a change in ankle, knee and/or hip angles, could reduce the demands or reliance placed on this muscle group for optimal control. This may be associated with a possible change, for example, to a more predominant hip control strategy.

Conclusion

The postural control of unipedal stance was more impaired when ankle PFs and DFs were fatigued simultaneously compared with separately. This observation was only true with eyes closed, as vision alleviated the instability induced by fatigue. Moreover, different posture control variables recovered at different rates following fatigue of ankle PFs and DFs.

Fig. 1 .

 1 Fig. 1. Schematic representation of the experimental procedure focusing on postural trials. EO: postural trials performed with eyes open. EC: postural trials performed with eyes closed. F1-F4: fatigue protocols. R: 60-s rest period between recovery trials.

Fig. 3 .

 3 Fig. 3. Sway area AE SD (A) and AP velocity AE SD (B) recorded during the three experimental sessions (PFs + DFs, PFs, DFs) performed with eyes closed before (PRE) and after (POST) the fatigue protocol. ***Significant differences between PRE and POST (p < 0.001).

Fig. 2 .

 2 Fig. 2. Sway area AE SD recorded during the three experimental sessions (PFs + DFs, PFs, DFs) performed with eyes open (EO) and with eyes closed (EC). **Significant differences between experimental sessions (p < 0.01). The significant (p < 0.001) differences between EO and EC trials of the same experimental sessions were not represented for clarity.

Fig. 4 .

 4 Fig. 4. Changes in sway area AE SD (A), AP velocity AE SD (B), and AP position AE SD (C) for the PFs + DFs experimental session, eyes closed condition. PRE: pre-fatigue data. POST: post-fatigue data. R1-R8: data recorded after the first to the eighth recovery periods. ***Significantly different from other data (p < 0.001). Considering AP position, positive changes indicate a forward displacement of the COP whereas negative changes indicate a backward displacement.

Table 1

 1 Durations and number of contractions of the fatigue tests (mean AE SD).

		PFs + DFs		PFs		DFs
		Duration (s)	Number of contractions	Duration (s)	Number of contractions	Duration (s)	Number of contractions
	Fatigue test 1	122.6 AE 67.9	69.1 AE 40.9	60.0 AE 19.8	37.7 AE 12.3	76.1 AE 39.4	76.0 AE 36.8
	Fatigue test 2	90.3 AE 48.6	53.2 AE 31.9	56.3 AE 19.8	36.6 AE 12.2	75.0 AE 52.3	82.4 AE 62.1
	Fatigue test 3	81.8 AE 44.1	49.4 AE 26.3	51.9 AE 20.7	34.1 AE 12.8	63.6 AE 43.9	70.8 AE 50.1
	Fatigue test 4	76.8 AE 38.5	48.6 AE 26.2	67.6 AE 20.4	44.4 AE 17.2	69.2 AE 56.4	80.7 AE 71.1
	Mean AE SD	92.9 AE 52.9 *	55.1 AE 42.2	58.9 AE 28.9	38.2 AE 15.4	71.0 AE 47.6	77.5 AE 43.1 *
	* Significantly different (p < 0.05) from PFs session.

Table 2

 2 Results of the three-way ANOVAs (vision  fatigue  muscle group) for the five postural variables.

		Sway area		ML velocity		AP velocity		ML position	AP position
		F	p	F	p	F	p	F	p	F	p
	Vision (V)	119.3	<0.001	146.7	<0.001	98.6	<0.001	ns		ns
	Fatigue (F)	15.5	0.004	ns		29.4	<0.001	ns		21.2	0.002
	Muscle group (MG)	ns		ns		ns		ns		ns
	V Â F	35.6	<0.001	ns		22.1	0.002	ns		ns
	V Â MG	4.9	0.022	ns		ns		ns		ns
	F Â MG	ns		ns		ns		ns		ns
	V Â F Â MG	ns		ns		ns		ns		ns
	ns: non significant.

Acknowledgements

This study was funded in part by the Natural Sciences and Engineering Research Council of Canada (Discovery Grant # 312041-2008 to M. Bilodeau) and the Canada Foundation for Innovation (Leaders Opportunity Fund Award to M. Bilodeau).

Conflict of interest

None of the authors have ties to any activity or industry that could inappropriately influence his judgment regarding this research or the results presented in the manuscript.


Cinematic and geomorphological study of the Mare a Poule d'Eau landslide (Hell-bourg, La Reunion island) using satellite (SPOT5) and aerial images Rejanne Le Bivic

Introduction

La Réunion is a volcanic island located in the Indian Ocean. Its climate is tropical . This island is characterized by pluviometric records with an annual cumulative rainfall locally exceeding 7m/year. The main precipitations occur during intense rainfalls often linked to cyclones in the winter season. These extreme events, combined to steep slopes, lead to an intense erosion.

The slow-moving landslide of Mare à Poule d'Eau (MAPE) located in the Salazie watershed is the result of a massive debris avalanche due to the dismatling of the extinct volcano (Piton des Neiges) 955 000 years ago (Arnaud, 2005). The permanent GNSS receivers network (BRGM-French Geological Surveys) shows a maximum velocity of 1,7 m/year for the 2010-2013 period. The Northern limit of the landslide is the River du Mât, a permanent river which mean annual ow is 3m 3 /s and can reach 145 m 3 /s during cyclones.

Contact :

Réjanne LE BIVIC rejanne.lebivic@gmail.com General velocities are over-estimated (compared to the velocity measured using the permanent GNSS receivers network) : -Uncertainties of the correlation method : 1/10 pixel (which is equal to an error of 0.35m/year); -Rapid changes in vegetation may induce errors.

Directions (6) :

the landslide main direction as measured by the BGRM -French Geological Surveys is North, which is the main direction calculated correlating SPOT5 images. However this methods show the e ects of the river at the Northern limit of the landslide. Despite those local extremes the directions vary from N335° to N25°.

Bibliography and aknowledgements

In order to derive surface displacement maps, correlation of SPOT5 images has been applied on images pairs using the MicMac software (Deseilligny et al., 2013). This correlation is challenging on tropical areas due to high seasonal vegetation changes. Due to high relief only images acquired with a similar phase angle have been processed.

Stability of the landslide limits:

-no retrogressive erosion at the landslide' limits -retrogressive erosion of 120m (1) : the main source of sediments for the river

The aim of this study is to improve the knowledge of this landslide combining : -a cinematic study of the landslide from SPOT5 images correlation and IGN images observation -a geomorphological study to combine those results to the morphology of the landslide and improve our knowledge on the landslide/river interface

(1)

  Cinematic and geomorphological study of the Mare a Poule d'Eau landslide (Hell-bourg, La Reunion island) using satellite (SPOT5) and aerial images Réjanne LE BIVIC 1 , Amélie QUIQUEREZ 2 , Pascal ALLEMAND 3 , Christophe DELACOURT 1 1 : Laboratoire Domaines Océaniques, UMR 6538, IUEM, BREST, FRANCE 2 : ARTEHIS, UMR CNRS 6298, Université de Bourgogne 21000 DIJON, FRANCE 3 : Laboratoire Sciences de la Terre, UMR 5570, Université Claude-Bernard Lyon 1. 2 rue Raphael Dubois, VILLEURBANNE, FRANCE Context of the study II. Geomorphological study of the landslide (1949-2011) I. Cinematic study of the landslide using SPOT5 images correlation (2002-2014) General tendencies : -the interval 2006-2008 is a period of intense horizontal displacement, probably due to the cyclone Gamede in 2007; -the best results are obtained correlating images acquired during the same season; -higher velocities are calculated on the North-Eastern part of the landslide. Relation between horizontal displacement and pluviometry : high cumulated rainfalls lead to a more important displacement than the intensity of the rainfall event itself.

I. 2 .

 2 Temporal evolution of the landslide horizontal velocity (2003-2012) I. 1. Main slip surface : spatial variability of the horizontal displacement II. 2. River/landslide interactions : evolution of the active river bed II. 1. Geomorphology of the limits of the landslide from aerial images We would like to thank the CNES for providing SPOT5 images through the Isle-Kalideos program and for nancially supporting this work through the TOSCA program. This work is nancially supported by the EU through the FP7 project IQmulus (FP7-ICT-2011-318787). The pluviometric data are provided by the French Meteorological Institute Météo France. Arnaud, N., 2005. Les processus de démantèlement des volcans, le cas d'un volcan bouclier en milieu océanique : le Piton des Neiges (ile de la Réunion). PhD, Univ. of la Reunion. Deseilligny, M.-P., Belveaux, J., Choqueux, G., Deveau, M., Girod, L., 2013. MicMac, Apero and Other Beverages in a Nutshell, ENSG -Marne-la-Vallée. p. 275.

  S t a b l e r i v e r / l a n d s l i d e i n t e r a c t i o n z o n e M o b i l e z o n e Stability of the river bed : quick return of the river to its equilibrium state after a ood. In uence : seasonnal oods Two in uences : -mostly landslide (advance towards the North) -powerful oods (punctual erosion, ten-yearly) Location of the study site : the Mare à Poule d'Eau landslide in La Reunion island (Indian Ocean) Mean velocities and directions of the slip surface calculated from 27 pairs of SPOT5 images using correlation techniques. Displacement between two images acquisitions : 2005-2006, 2006-2008 and 2011-2014 illustrating the temporal variability of the horizontal displacement (notice that the colorbar is speci c to each image) Monthly rainfalls recorded in Hell-bourg and Salazie stations from 2002 to 2014. Surface of the active river bed from aerial images, from 1949 to 2011 River/landslide interface observed from aerial images from 1949 to 2011 Evolution of the crests and increase of the vegetation from 1949 to 2011 due to a revegetation policy


••

  Etudes rapportant un ratio différentiel coût-résultat (efficacité ou utilité) de la TM par SR ± TIV, comparée à la TIV seule • Qualité des études : grilles de CHEERS et de Philip's • Comparaison des coûts avec année de référence = 2016  Actualisation : parité de pouvoir d'achat  Conversion : indice des prix à la consommation de chaque pays Première revue systématique de la littérature sur les SR • Malgré des méthodologies hétérogènes, la stratégie SR + TIV versus TIV seule est plus efficiente, voire plus efficace et moins coûteuse (dominante) dans 3 des 7 études incluses • Paramètres les plus influents = durée de l'étude, coûts à long terme, probabilité d'être dépendant (mRS 4-5) à 90 jours • Coûts de transfert des patients vers une unité neurovasculaire non inclus Résultats • 7 études incluses (4 nord-américaines/3 européennes) fondées sur des modèles coûts-utilités • Point de vue adopté : Assurance Maladie pour 6 études et société pour une étude • Qualité des études : bonne, score 79% [70-90] Congrès de la Société Française de Neuro-Vasculaire, 15-17 novembre 2017 Période = 2009  2016 Veille biblio BOUDOUR S. (1), BARRAL M. (2), GORY B. (3), SCHOTT AM (2), VIPREY M. (2), ARMOIRY X. (1) (1) Service Pharmacie -Hospices Civils de Lyon, UMR-CNRS 5510, MATEIS Université Claude Bernard Lyon 1, Bron, France (2) Hospices Civils de Lyon, Pôle IMER, Lyon, France ; Univ. Lyon, Université Claude Bernard Lyon 1, HESPER EA 7425, Lyon, France (3) Service de Neuroradiologie Interventionnelle -Hospices Civils de Lyon, Hôpital Pierre Wertheimer, FHU IRIS, Bron, France

  Incremental Cost Effectiveness Ratio ; QALY = Quality Adjusted Life Years


Romain Boyer

Frédéric Camps

Khalil Drira

Ghada Gharbi

Thomas Boursac

Poster Conceptualization and Specification of the Machine-to-Machine Payload System on NIMPH Satellite for IoT-Based Medical Monitoring Applications

établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

M2M (Machine to Machine) payload -SARA Team LAAS-CNRS, Université de Toulouse, CNRS, EPITA, Toulouse, France Thomas Boursac, Frédéric Camps, Ghada Gharbi, Khalil Drira, Romain Boyer / Contact fcamps@laas.fr

M2M (NIMPH Payload):

The NIMPH project's M2M system is designed to establish efficient, reliable, long-range communication between IoT devices and servers via a nanosatellite. The heart of the system is the NIMPH M2M payload, which enables data transmission between IoT devices and servers via satellite links.

M2M Gateway

IoT#1 Medical center

IoT#3 IoT#2 M2M Gateway M2M Gateway

Objectives:

➢ The scientific challenges for IoT and M2M protocols in space are linked to the unique environmental conditions of space, the need to optimize the management of limited resources, and the reliability and security of space communications.

➢ Researchers and engineers are actively working on these challenges to enable the effective use of these technologies in space exploration and satellite management.

SCC ground station:

• The ground station used to communicate with the satellite is the SCC (Simple Control Center). • The generic structure of a CCSDS 133.0-B-1 packet is described below.

Packet Primary Header Packet data field

M2M <-> PUS conversion:

• There is no actual M2M to PUS converter.

• The M2M data is inserted in raw form into the PUS frame data. • This data is then sent back to the gateways.

Advantages:

• Satellite invariance to terrestrial protocol: a protocol other than M2M could be used on the ground. • Reduced on-board complexity: reduced risk to flight software • Fast satellite processing: no M2M frame deconstruction.

Partition M2M:

The M2M partition within the NIMPH satellite is programmed to respond to different types of communications from the ground station (GS):

➢ TC_133_1_DATA_M2M: Sending a packet for registration in the packet list ➢ TC_133_2_GET_DATA_M2M: Transmits packet request for destination as argument Its response will then be a telemetry of the desired packets. ➢ TM_133_3_MESSAGE_M2M: Returns the TMs containing the packets requested by TC_133_2.

Support Hardware M2M:

• The M2M payload is purely software.

• It does not require a specific electronic board within the satellite.

• Its program will be stored in the on-board computer (Ninano card) as a separate partition.

• The on-board computer will execute this payload according to its schedule of tasks to be performed (avionics, payloads, etc.).

Medical Use case

Architecture:

• NIMPH M2M Payload: An essential component of the NIMPH satellite, its main purpose is to manage Machine-to-Machine (M2M) communications between Internet of Things (IoT) devices and various IoT systems via the NIMPH satellite.

• Generic gateway, IoT gateway: a device designed to act as an intermediary between IoT devices and the NIMPH M2M payload. It is modular to adapt to different ground protocols, and enables IoT devices to communicate seamlessly with NIMPH.

• Ground IoT systems: technological infrastructure that collects, processes and manages data generated by connected objects, ensuring their communication with other systems and applications.

• Each IoT device may or may not be permanently connected to a gateway for data transfer to satellites (M2M PUS conversion).

  NIMPH is an academic research project led by the Centre Spatial Universitaire de Toulouse (CSUT). It involves numerous Master's students from Paul Sabatier University (UPS) and the ENSEEIHT engineering school, mainly through internships, research projects and practical work, under the supervision of professors and permanent staff from LAAS -CNRS.Nanosatellite characteristics :▪ Volume 3U (300 cm 3 ) ▪ Weight 2 kg ▪ UHF radio (430MHz) ▪ Sun-synchronous low-Earth orbit ▪ Power consumption: 7 W ▪ Mission duration: 2 years ▪ 3 payloads: EDMon, RADMon, M2M ▪ C phase Ground station and PUS protocol: Flight program: Objectives and system architecture: