Kinetics and kinematics of strength and power development
The use of the squat exercise (and its derivatives) in gym-based settings is widespread owing to perceived functional performance enhancing effects. In particular, there has been preponderance amongst practitioners with loads that maximise power outputs (Pmax) based on a perception that mechanical peak power is directly related to explosive functional performance such as sprinting ability. The optimal muscular quality associated with squats remains elusive though, mostly due to methodological limitations in the research. The four experimental studies in this thesis sought to quantify the kinetic and kinematic outputs of a machine squat-jump and their relationship to sprinting ability, both descriptively and across a training period. First, an analysis of the kinetic and kinematic outputs of a machine squat-jump across a spectrum of loads was performed, with an emphasis on power output. Then, the relationship of these outputs with sprint ability was investigated. Correlations do not imply cause and effect, thus a training intervention was undertaken to quantify the relationships of the change in performance measures over time, and allow a comparison of different training protocols. Specifically, one training group was prescribed training loads based on individually determined peak power outputs, and the other based on traditional maximal strength training loads. Because the intention of this thesis was to enhance our knowledge of best strength training practice for elite sporting performance, highly trained athletes were specifically chosen as subjects, cognizant of the population specific nature of training adaptation. In study one, it was determined that the point on the power-load spectrum where peak and mean power occurred in the machine squat-jump was 21.6 ± 7.1 %1RM (mean ± SD) and 39.0 ± 8.6 %1RM respectively although there was considerable individual variation in these points. A broad plateau in power outputs was evident for most subjects with at most a 9.9% (90% confidence limits ±2.4%) difference in peak or means power at loads up to 20 %1RM either side of the peak. Studies two and three established that, of the multiple kinetic and kinematic measures investigated, only 1RM strength, work and impulse (all relative to body mass) provided any indication of useful kinetic / kinematic outputs that were potentially worthwhile developing for enhancing sprint performance, albeit with only moderate correlations (r = ~ -0.3). Additionally, the intercorrelations between maximal strength and explosive kinetic and kinematic measures were only moderate (r = ~0.3), casting doubt on the common practice of pursuing high 1RM strength with the intention of improving explosive muscle performance. The training study provided evidence that training at the load that maximised individual peak power output was no more effective for improving sprint ability than training at heavy loads and the changes in kinetic and kinematic outputs were not usefully related to changes in sprint ability.