Timing of lower extremity motions during barefoot and shod running at three velocities

Utilisation d'images vidéo digitalisées pour étudier les différences de timing des mouvements de l'articulation de la cheville et de celle du genou chez 9 coureurs de fond effectuant des courses de 30 mètres sur piste indoor à la vitesse de 3,5 ou 4,5 ou 5,5 mètres par seconde

The influence of an increased take-off on mechanical and kinesiological variables in high jumping

The purpose of this study was to investigate if jumping off from a flat take-off support, 0,29 m above the ground, influences specific mechanical and kinesiological variables during the take-off phase. Method 7 male experienced high jumpers (age: 25±6 years; height: 1,88±0,03 m; weight: 75,3±3,3 kg) were filmed doing maximum jumps with normal and increased take-off (height : 0,29 m). Mechanical (movement of C.0.G) and kinesiological (body segment interaction) variables were analysed and compared for both conditions (Wilcoxon). Results and discussion a Mechanical : There is a tendency to a larger maximum flight height of the center of gravity, when jumping with an increased take-off (normal : 1,99 f 0,13 m ; increased: 2,03 ±0,13 m ; NS). This is in contrast with the normal take-off which shows a larger linear impulse, resulting in larger vertical (normal : 3,96 ±0,39 m. s&#713;¹; increased: 3,16 ±0,30 m. s&#713;¹; p < 0,05) and horizontal (normal : -2,99±0,40 m. s&#713;¹; increased: -2,83 ±0,31 m. s&#713;¹; NS) changes in velocity during the last contact. When jumping off from the increased take-off, the linear impulse is less because the C.O.G. obtained already a positive vertical velocity (0,64 ±0,10 m.s s&#713;¹ ) in the second last step. b. kinesiological : The average radial velocity of the hip of the take-off leg is more negative with a normal take-off (-3,33 f 0,36 m. s&#713;¹increased : -3,02 f 0,25 m. s&#713;¹; NS) , and reaches also later a positive value, which points to a larger eccentric load of the knee extensor muscles. Normal take-off also shows larger values of the velocity of the knee angle, as well in eccentric (maximal flexion velocity : normal : -621 ±78,8 degrees. s&#713;¹; increased : -581±32,3 degrees.s&#713;¹;N S) as in concentric status ( normal : 413,4 ±112,7 degrees. s&#713;¹ ; increased : 315,l ±71,6 degrees. s&#713;¹; p < 0,05). The eccentric-concentric coupling is fluent, while with an increased take-off the knee remains maximally flexed for a rather large period (30 ms). The radial velocity of the swinging leg also contributes to the eccentric-concentric cycle. Conclusion High jumping with an increased take-off tends to lead to a higher jump, probably with a smaller loading of the take-off leg. This can be explained by a more pronounced pre-take-off during the second last foot contact