Adaptations neuromusculaires des muscles extenseurs du genou (contractions fatigantes uni- vs bi-latérales)

L objectif de ce travail était de déterminer i) l influence du niveau de force absolue sur la durée du temps de maintien, et les altérations neuromusculaires subséquentes chez un même individu à l issue d un exercice réalisé à la même intensité relative, avec un ou deux membres ; ii) l influence de la commande nerveuse sur la capacité de production de force de chacun des muscles extenseurs du genou lors de contractions unilatérales (UL) vs. bilatérales (BL); iii) l évolution des mécanismes d activation pendant une série de contractions sous-maximales évoquées par électromyostimulation (EMS).Les résultats de la première étude confirment que le temps limite est dépendant du niveau de force absolu pour un même individu, la durée de la contraction en UL étant 20% plus longue qu en BL. De plus, une corrélation a été trouvée entre la force lors d une contraction maximale volontaire (CMV) et le temps limite en UL et BL. Toutefois, d autres mécanismes semblent être également mis en jeu, car dans un cas les mécanismes sont d origine nerveux et musculaire (UL), alors que dans l autre cas les mécanismes sont seulement nerveux (BL). Les résultats de la deuxième étude montrent que la force maximale développée lors d une contraction BL est inférieure à la somme des forces des contractions UL (i.e. présence d un déficit bilatéral). Les temps d apparition des pics de force lors des CMV de chacune des jambes ne sont pas différents de celui de la CMV BL, mais la force développée au cours de celle-ci est inférieure à la somme des CMV de chacune des jambes durant la CMV BL, c'est-à-dire à la force maximale produite par chacune des jambes lors de la CMV BL. Néanmoins, aucune différence d activité EMG, d amplitude d onde M, de doublet et de niveau d activation n a été observée entre les conditions UL et BL. Les résultats de la troisième étude montrent que l estimation de la commande descendante, par la technique de la secousse surimposée, lors d un effort sous-maximal fatigant présente des biais méthodologiques. Toutefois, l estimation des mécanismes nerveux par les deux méthodes classiques (niveau d activation volontaire (NAV) et ratio d activation centrale (CAR)) reste néanmoins pertinente pendant des contractions maximales volontaires. L ensemble de nos travaux met en évidence l intervention de mécanismes d origine nerveux différents entre les contractions UL et BLThe aim of this work was to determine i) the influence of the level of absolute force on the duration of the endurance time, and subsequent neuromuscular alterations in same individual at the end of an exercise performed at the same relative intensity, with one or two legs, ii) the influence of central drive on the force capacity production of the knee extensor muscles during unilateral (UL) vs. bilateral (BL) contractions, iii) activation mechanisms evolution for a serie of submaximal evoked contractions by electrostimulation (EMS). The results of the first study confirm that the endurance limit depends on the level of absolute force for the same individual, contraction duration for UL is 20% longer than for BL. In addition, a correlation was found between the maximal voluntary contraction force (MVC) and the endurance time in UL and BL. However, other mechanisms also appear to be involved, because in one case the mechanisms are nervous and muscular (UL), while in other cases the mechanisms are only nervous (BL). The results of the second study show that maximal force developed during BL contraction is less than the sum of the forces of UL contraction (i.e. a bilateral deficit). The timing of MVC peak force production during each leg of MVC are not different from that of BL MVC, but the force developed during the latter is less than the sum of MVC in both legs during the BL MVC, i.e. the maximum force produced by each leg during BL MVC. However, no difference in EMG activity, M-wave amplitude, doublet and level of activation was observed between UL and BL conditions. The results of the third study show that the estimation of the central drive, by the technique of superimposed twitch during a submaximal fatiguing effort presents methodological bias. However, estimation of neural mechanisms with both conventional methods (voluntary level activation (VAL) and central activation ratio (CAR)) remains relevant during maximal voluntary contractions. This work évidences the presence of different nervous mechanisms between UL and BL contractionsDIJON-BU Doc.électronique (212319901) / SudocSudocFranceF

Age-related changes in 100-km ultra-marathon running performance

The aims of this study were (1) to investigate the participation and performance trends at the ‘100km Lauf Biel' in Switzerland from 1998 to 2010, and (2) to compare the age-related changes in 100-km running performance between males and females. For both sexes, the percent of finishers significantly (P < 0.01) decreased for the 18-29 and the 30-39-year age groups, while it significantly (P < 0.01) increased for the 40-49 and the 50-59-year age groups over the studied period. From 1998 to 2010, the mean age of the top ten finishers increased by 0.4years per annum for both females (P = 0.02) and males (P = 0.003). The running time for the top ten finishers remained stable for females, while it significantly (P = 0.001) increased by 2.4min per annum for males. There was a significant (P < 0.001) age effect on running times for both sexes. The best 100-km running times was observed for the age comprised between 30 and 49years for males, and between 30 and 54years for females, respectively. The age-related decline in running performance was similar until 60-64years between males and females, but was greater for females compared to males after 65years. Future studies should investigate the lifespan from 65 to 75years to better understand the performance difference between male and female master ultra-marathoner

Swimrun:an emerging new endurance sport

The swimrun is a new endurance team-sport based on two persons swimming and running alternatively through open water and mostly trails. The aim of this study was to analyse participation and performance trends for males, females and mixed duo team at the ÖTILLÖ Swimrun race (10km open-water swimming and 65km trail running). During the 2012-2016 period, the mean total time performance of the best athletes at the ÖTILLÖ Swimrun decreased significantly by 17 min/year for males, 40 min/year for mixed and 59 min/year for females duo, respectively. The difference in performance between the best males and females duo (26±15%) was significantly greater compared to the difference between males and mixed duo (12±8%). The number of swimrun races organized across the world has dramatically increased these last years and will probably continue to grow up in the future. Swimrun athletes are still not very experienced, thus both improvements in performance and reduction in sex difference are expected in the next decade

Wheelchair half-marathon and marathon performance – the ‘Oita International Wheelchair Marathon’ 1983-2011

We compared participation and performance trends of individuals with disabilities competing in the half- and full-marathon in the ‘Oita International Wheelchair Marathon’ from 1981 to 2011. The performance times decreased during the 1980’s until the middle 1990’s and stabilized thereafter for both half-marathoners and marathoners. The mean top five overall finishers times were 0:52±0:07 h:min for half-marathoners and 1:36 ±0:11 h:min for marathoners, respectively. The mean age of the finishers increased significantly (p < 0.01) by 0.51 year per annum for the half-marathoners and by 0.62 year per annum for the marathoners, respectively. There was a significant (p < 0.001) age effect on time performance for both distances. The best time performance was observed for the age comprised between 16 and 54 years for half-marathoners, and between 25 and 49 years for marathoners, respectively

The effects of course length on freestyle swimming speed in elite female and male swimmers - a comparison of swimmers at national and international level

Freestyle swimming performance over 50 m, 100 m, 200 m, 400 m, 800 m and 1,500 m was compared on short (25 m) and long (50 m) course for 92,196 national swimmers (i.e. annual high score list Switzerland) and 1,104 international swimmers (i.e. finalists FINA World Championships) from 2000 to 2012. National and international swimmers of both sexes were on average 2.0 ± 0.6% faster on short than on long course. Sex-related differences in swimming speed were greater on short than on long course for international and national swimmers from 50 m to 800 m. Freestyle swimming performance improved across years for international swimmers in both short- and long-course whereas only male national swimmers were able to improve on short and long course events except for short course events on 800 m and 1,500 m. Performance in national women competing in short and long course events showed only improvements on 50 m, 100 m and 1,500 m across years. The sex-related differences in freestyle swimming performance showed no change for international swimmers. For national swimmers, the sex-related differences in freestyle swimming performance increased over time in long course from 50 m to 800 m, but decreased for 1,500 m. In conclusion, elite female and male freestyle swimmers at national and international level were about 2% faster on 25 m compared to 50 m course. During the 2000-2012 period, international as well as national swimmers (i.e. for national level predominantly men) improved freestyle swimming performance in both long and short course. More vigorous and optimized training programs focused on muscular force production in combination with efficient swimming skills might close the performance gap between elite swimmers at national level and FINA finalists. Further research especially including effects of anthropometric, biomechanical, and physiological factors is required to fully understand the effects of course length on freestyle swimming performance, and to determine whether course length has similar effects on other swim styles

Elite triathletes in ‘Ironman Hawaii' get older but faster

The age of peak performance has been well investigated for elite athletes in endurance events such as marathon running, but not for ultra-endurance (>6h) events such as an Ironman triathlon covering 3.8km swimming, 180km cycling and 42km running. The aim of this study was to analyze the changes in the age and performances of the annual top ten women and men at the Ironman World Championship the ‘Ironman Hawaii' from 1983 to 2012. Age and performances of the annual top ten women and men in overall race time and in each split discipline were analyzed. The age of the annual top ten finishers increased over time from 26 ± 5 to 35 ± 5years (r 2 = 0.35, P < 0.01) for women and from 27 ± 2 to 34 ± 3years (r 2 = 0.28, P < 0.01) for men. Overall race time of the annual top ten finishers decreased across years from 671 ± 16 to 566 ± 8min (r 2 = 0.44, P < 0.01) for women and from 583 ± 24 to 509 ± 6min (r 2 = 0.41, P < 0.01) for men. To conclude, the age of annual top ten female and male triathletes in the ‘Ironman Hawaii' increased over the last three decades while their performances improved. These findings suggest that the maturity of elite long-distance triathletes has changed during this period and raises the question of the upper limits of the age of peak performance in elite ultra-endurance performance

Neuromuscular and Perceptual Responses to Sub-Maximal Eccentric Cycling

ObjectiveEccentric (ECC) cycle-ergometers have recently become commercially-available, offering a novel method for rehabilitation training. Many studies have reported that ECC cycling enables the development of higher levels of muscular force at lower cardiorespiratory and metabolic loads, leading to greater force enhancements after a training period. However, fewer studies have focused on the specific perceptual and neuromuscular changes. As the two latter aspects are of major interest in clinical settings, this review aimed to present an overview of the current literature centered on the neuromuscular and perceptual responses to submaximal ECC cycling in comparison to concentric (CON) cycling.DesignNarrative review of the literature.ResultsAt a given mechanical workload, muscle activation is lower in ECC than in CON while the characteristics of the musculo-articular system (i.e., muscle-tendon unit, fascicle, and tendinous tissue length) are quite similar. At a given heart rate or oxygen consumption, ECC cycling training results in greater muscular hypertrophy and strength gains than CON cycling. On the contrary, CON cycling training seems to enhance more markers of muscle aerobic metabolism than ECC cycling performed at the same heart rate intensity. Data concerning perceptual responses, and neuromuscular mechanisms leading to a lower muscle activation (i.e., neural commands from cortex to muscular system) at a given mechanical workload are scarce.ConclusionEven though ECC cycling appears to be a very useful tool for rehabilitation purposes the perceptual and neural commands from cortex to muscular system during exercise need to be further studied

Participation and Performance Trends in Triple Iron Ultra-triathlon - a Cross-sectional and Longitudinal Data Analysis

PURPOSE: The aims of the present study were to investigate (i) the changes in participation and performance and (ii) the gender difference in Triple Iron ultra-triathlon (11.4 km swimming, 540 km cycling and 126.6 km running) across years from 1988 to 2011. METHODS: For the cross-sectional data analysis, the association between with overall race times and split times was investigated using simple linear regression analyses and analysis of variance. For the longitudinal data analysis, the changes in race times for the five men and women with the highest number of participations were analysed using simple linear regression analyses. RESULTS: During the studied period, the number of finishers were 824 (71.4%) for men and 80 (78.4%) for women. Participation increased for men (r(2)=0.27, P<0.01) while it remained stable for women (8%). Total race times were 2,146 ± 127.3 min for men and 2,615 ± 327.2 min for women (P<0.001). Total race time decreased for men (r(2)=0.17; P=0.043), while it increased for women (r(2)=0.49; P=0.001) across years. The gender difference in overall race time for winners increased from 10% in 1992 to 42% in 2011 (r(2)=0.63; P<0.001). The longitudinal analysis of the five women and five men with the highest number of participations showed that performance decreased in one female (r(2)=0.45; P=0.01). The four other women as well as all five men showed no change in overall race times across years. CONCLUSIONS: Participation increased and performance improved for male Triple Iron ultra-triathletes while participation remained unchanged and performance decreased for females between 1988 and 2011. The reasons for the increase of the gap between female and male Triple Iron ultra-triathletes need further investigations