Stéphane Champely

Fixed versus free-floating stretcher mechanism in rowing ergometers: Mechanical aspects

Abstract The mechanical responses (i.e. external contact forces and external power) of 25 elite rowers to a race-pace rowing protocol were investigated on the traditional fixed stretcher mechanism and the more recently introduced free-floating stretcher mechanism rowing ergometers. Using a Rowperfect rowing ergometer for both conditions, external contact forces at the handle, stretcher and sliding seat, as well as the displacements of the handle and stretcher, were recorded. The external power was calculated as the product of the force and velocity data from both the handle and stretcher. Significant differences (P < 0.05) between the two conditions for each mechanical parameter were observed. The fixed condition showed larger maximum values for forces and external power and average power throughout the rowing cycle. Moreover, rowing with the fixed mechanism generated higher inertial forces during the transition between the propulsion and recovery phases, especially at the catch of the cycle. The results suggest that: (i) muscular coordination may differ according to the stretcher mechanism used, which could have an impact on the physiological adaptations of muscles; and (ii) the free-floating mechanism may induce lower catch and maximum values for net joint forces and net joint moments that could decrease the risk of injury.

Age determination in leverets of European hare Lepus europaeus based on body measurements

The objective of our work was to provide allometric relationships between different body measurements and age of young leverets of European hare Lepus europaeus (less than two months old) for use in live-trapping studies. Five morphometric variables were measured to predict the age of leverets: body mass, skull length, skull width, hind foot length and ear length. The hares came from two rearing centres near Paris (France) and were handled in 1995 and 1996. Measurement repeatability of each variable was compared in a pilot study (N = 51 leverets) and the effect of rearing centre on the growth curve was tested for the first 30 days after birth. We used a complementary sample (N = 168 leverets) to establish a model of age determination using I-splines regression. The skull length was the best candidate variable based on measurement repeatability, comparability between the two rearing centres and goodness of fit. I-spline modelling has minimal underlying statistical assumptions. In addition, it provides easy-to-use and powerful plots of the relation between age and measurements, including confidence limits estimated by a bootstrap procedure.

Reliability of EMG normalisation methods for upper-limb muscles.

Abstract The study investigated different electromyographic (EMG) normalisation methods for upper-limb muscles. This assessment aimed at comparing the EMG amplitude and the reliability of EMG values obtained with each method. Eighteen male tennis players completed isometric maximal voluntary contractions and dynamic strength exercises (push-ups and chin-ups) on three separate test sessions over at least 7 days. Surface EMG activity of nine upper body muscles was recorded. For each muscle, an analysis of variance for repeated measures was used to compare maximal EMG amplitudes between test conditions. The intra-class correlation coefficient, the coefficient of variation and the standard error of measurement were calculated to determine the EMG reliability of each condition. On the basis of a compromise between maximal EMG amplitude and high reliability, the chin-ups appeared to be the optimal normalisation method for M. latissimus dorsi, M. posterior deltoid, M. biceps brachii, M. flexor carpi radialis and M. extensor carpi radialis. The push-ups seemed relevant to normalise M. anterior deltoid and M. triceps brachii activity, while isometric maximal voluntary contraction remained the most appropriate method for M. pectoralis major and M. middle deltoid. Thus, original methods are proposed to normalise EMG signal of upper-limb muscles.

Motor imagery effectiveness for mirror reversed movements.

Physical practice is known to enhance motor adaptation skills, which refer to the individual ability to compensate for environmental changes. So far, it is still unknown whether a similar effect can be observed following motor imagery (MI). Thirty-nine participants were tested during a joystick tracking task under both normal and mirror conditions (i.e., the inductive direction of the joystick was reversed), before and after a physical practice or MI training phase. Eye movements and electromyographic activity were recorded during MI. Motor performance was also evaluated after a 6xa0h interval during daytime. As compared to the control group, the results revealed that both MI and physical practice improved motor performance in the mirror condition, during the post-training test. Furthermore, the time to complete the task was further reduced after 6 hours, both in the normal and mirror conditions. These results demonstrate the effectiveness of MI for learning mirror-reversed movements, and for the consolidation process that follows motor adaptation.

La pratique physique, un moyen de circonscrire les effets délétères du confinement en milieu carcéral : impact d’un programme d’activités physiques sur la santé perçue et le bien-être psychologique de détenus

Resume La prison represente un contexte aversif, constitue de multiples stresseurs et contraintes. Cette situation, imprevisible et incontrolable pour les detenus, combinee a des conditions de detention souvent penibles, genere des difficultes sanitaires pesantes et une detresse certaine chez ses occupants. Compte tenu des bienfaits sanitaires conferes aux Activites Physiques et Sportives (APS), il est alors legitime d’envisager leurs possibles apports en detention, dans une perspective de promotion de la sante, bien que peu de travaux ne soient encore disponibles pour en attester. La presente etude rend compte des benefices sanitaires de ces activites en prison et confirme les bienfaits d’une pratique physique saine et raisonnee sur la sante percue et le bien-etre psychologique de detenus particulierement necessiteux, les delinquants sexuels.

Effects of Age and Task Load on Drivers’ Response Accuracy and Reaction Time When Responding to Traffic Lights

Due to population aging, elderly drivers represent an increasing proportion of car drivers. Yet, how aging alters sensorimotor functions and impacts driving safety remains poorly understood. This paper aimed at assessing to which extent elderly drivers are sensitive to various task loads and how this affects the reaction time (RT) in a driving context. Old and middle-aged people completed RT tasks which reproduced cognitive demands encountered while driving. Participants had to detect and respond to traffic lights or traffic light arrows as quickly as possible, under three experimental conditions of incremental difficulty. In both groups, we hypothesized that decision-making would be impacted by the number of cues to be processed. The first test was a simple measure of RT. The second and third tests were choice RT tasks requiring the processing of 3 and 5 cues, respectively. Responses were collected within a 2 s time-window. Otherwise, the trial was considered a no-response. In both groups, the data revealed that RT, error rate (incorrect answers), and no-response rate increased along with task difficulty. However, the middle-aged group outperformed the elderly group. The RT difference between the two groups increased drastically along with task difficulty. In the third test, the rate of no-response suggested that elderly drivers needed more than 2 s to process complex information and respond accurately. Both prolonged RT and increased no-response rate, especially for difficult tasks, might attest an impairment of cognitive abilities in relation to aging. Accordingly, casual driving conditions for young drivers may be particularly complex and stressful for elderly people who should thus be informed about the effects of normal aging upon driving.

Driving Assistance during Bus Docking and Mental Load

The aim of the experiment was to test the effect of an automated system of bus docking on drivers mental workload, to guarantee good acceptance and minimal distraction from traffic. Reduced workload is thought to be brought about by helping the driver to maneuver, as he is only required to monitor proper functioning of the system. Workload was estimated by electrodermal activity recording while drivers tested five scenarios, involving or not the docking system. Results showed that docking precision was improved by the system, compared with manual docking. Drivers workload was higher when they monitored the functioning of the system but was reduced after a learning process. Increased workload was evidenced in the event of dysfunction of the docking system, especially when drivers had to take over control. However, after habituation, such a system could be integrated into buses to improve safety during boarding and egress.