A biomechanical analysis of maximum vertical jumps and sit to stand

by Domire, Zachary J.

The dissertation is made up of four reports, prepared in the format of journal manuscripts. Only the final report deals directly with the purpose of this dissertation, to develop a simulation of sit to stand that can be used to examine performance of the sit to stand in the elderly, and exploited to examine the influence of strength training on sit to stand performance in the elderly. The other three studies were used for the development of the simulation model. The first study investigated the effect of squat depth on jump height. Experimental subjects showed no difference in jump height in jumps from the deep and preferred positions. The optimal squat depth for the simulated jumps was the lowest position the model was able to jump from. Because jumping from a deep squat is rarely practiced, it is unlikely that these jumps are optimally coordinated. The second study examined how arm swing contributes to maximum vertical jump height. There was an increase in jump height with arm swing. The vertical velocity of the arms relative to the shoulder at takeoff was large enough to account for the performance enhancement. The work produced by the shoulder extensors was more than sufficient to explain the increase in jump performance. The work produced by the lower extremity muscles was slightly reduced in jumps with arm swing. The third study investigated the effect of chair height on sit to stand mechanics. It was found that forward trunk movement prior to seat off decreased as seat height decreased. This is the result of a higher initial hip angle in trials from low seat heights and forward trunk movement moving the hip extensors to a less favorable region of the force-length curve. The reduction in trunk movement prior to seat off increases the load on the knee extensors, which are already heavily burdened as a result of high initial knee angles. The fourth study examined the effect of strength training individual muscle groups on sit to stand performance. It was found that strength training the hip extensors and the knee extensors produced similar improvements in performance. These improvements were approximately one half of the improvement seen when training all muscles. There was potentially better control of the movement when all muscle groups iii were trained; as demonstrated by a reduction in peak joint extension angular velocities and a change in the timing of the maximum horizontal momentum. The results of these simulations suggest it is important to train all of the muscles rather than one specific muscle group for improving sit to stand performance. iv