| Summary |
Recent evidence shows that trunk flexion angle (TFA) affects hip extensor efforts during landing. Based on a kinetic-chain approach, decreased TFA during landing could lead to decreased hip work but increased knee and ankle work during jumping. However, the effect of TFA on LE energetics during a drop-jump is untested. Sex differences exist in landing where females primarily land with a knee and ankle dominant strategy. As it is also suggested that females land with an extended trunk, and TFA is correlated with hip work, TFA may explain the sex differences in LE muscle function during a drop- jump task. The purposes of this thesis were to examine: 1) sex differences on TFA, LE energetics, and maximal jump height, and 2) the effects of TFA on LE energetics and maximal jump height both during a drop-jump task. Twenty-four college-aged subjects (12 males/12 females) performed a drop-jump task while instrumented for biomechanical analysis. Subjects were grouped based on sex (hypothesis 1) and peak TFA (hypothesis 2). A t-test determined differences in mean peak TFA between sex and groups. Mixed-model ANOVAs were used for each hypothesis on LE dependent variables (a=.05). Peak TFA did not differ between males and females (-42.9° vs. -42.2°). A phase*sex interaction (p=0.011) showed that males increased the work done from deceleration to acceleration (-16.59J to 19.26J) while females did not (-16.20J to 15.88J). Males did more total work (35.85J vs. 32.80J) and jumped higher than females (0.53m vs. 0.33m; p<0.0001). A group*joint interaction (p=.013) showed that trunk flexors did more work at the hip (11.05J) and knee (13.21 J) than the ankle (8.19J) while trunk extensors did more work at the knee (13.80J) than the hip (9.40J) or ankle (10.10J). Groups did not differ in total work (33.93J vs. 34.01J; p=0.968) or maximal jump height (0.23m vs. 0.25m; p=0.651). Sex differences in LE work is not attributed to TFA. Males increase work during acceleration vs. deceleration while females do not. While TFA does not affect the total work throughout a drop-jump, the trunk flexors exhibited a hip and knee dominant strategy, while trunk extensors utilized a knee dominant strategy. |
