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. sˉ¹; increased: 3,16 ±0,30 m. sˉ¹; p < 0,05) and horizontal (normal : -2,99±0,40 m. sˉ¹; increased: -2,83 ±0,31 m. sˉ¹; 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 sˉ¹ ) 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. sˉ¹increased : -3,02 f 0,25 m. sˉ¹; 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. sˉ¹; increased : -581±32,3 degrees.sˉ¹;N S) as in concentric status ( normal : 413,4 ±112,7 degrees. sˉ¹ ; increased : 315,l ±71,6 degrees. sˉ¹; 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.