The rebound of the body during uphill and downhill running at different speeds.

When running on the level, muscles perform as much positive as negative external work. On a slope, the external positive and negative work performed are not equal. The present study analysed how the ratio between positive and negative work modifies the bouncing mechanism of running. Our goals are to: (1) identify the changes in motion of the centre of mass of the body associated with the slope of the terrain and the speed of progression, (2) study the effect of these changes on the storage and release of elastic energy during contact and (3) propose a model that predicts the change in the bouncing mechanism with slope and speed. Therefore, the ground reaction forces were measured on 10 subjects running on an instrumented treadmill at different slopes (from -9 to +9 deg) and different speeds (between 2.2 and 5.6 m s(-1)). The movements of the centre of mass of the body and its external mechanical energy were then evaluated. Our results suggest that the increase in the muscular power is contained (1) on a positive slope, by decreasing the step period and the downward movements of the body, and by increasing the duration of the push, and (2) on a negative slope, by increasing the step period and the duration of the brake, and by decreasing the upward movement of the body. Finally, the spring-mass model of running was adapted to take into account the energy added or dissipated each step on a slope

Differences in salivary hormones and perception of exertion in elite women and men volleyball players during tournament.

BACKGROUND: Sports tournaments induce both psychological and physiological stress, which seems to be different between men and women. Competition induces anticipatory rises in testosterone and cortisol levels, which may affect performance and physical exertion during tournaments. The aim of this study was to compare the changes in salivary cortisol and testosterone concentrations between men and women during an official volleyball tournament and to test potential correlations between changes in these hormones and perceived exertion after match. METHODS: Three matches of each team were assessed in the group stage of the Men and Women South American Volleyball Championship. Salivary cortisol and testosterone levels were measured in the fasting state, before and after each match. The rate of perceived exertion (RPE) was assessed after each match. RESULTS: Fasting cortisol concentrations were higher in women than men (~25%, P<0.001) while fasting testosterone was higher in men than women (~46%, P<0.001). Cortisol concentration increased only after the second match in men (+53.7%, P<0.001). Testosterone concentration was low before and after the third match in men (P<0.001) while it was elevated after the third match in women (P=0.003). The rate of perceived exertion was correlated with the change in testosterone levels due to the matches in both women (r=0.33; P=0.04) and men (r=0.44; P=0.02), which was not observed for cortisol concentrations. CONCLUSIONS: These results indicate that women have higher fasting cortisol, but lower fasting testosterone concentrations than men during a volleyball tournament. Thus, hormonal responses of women and men are different and related to their effort during the matches