Date of Award

11-2003

Degree Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Biomechanics

Supervisor

James J. Dowling

Abstract

A dynamic ballistic elbow extension task was chosen to investigate the mechanisms responsible for achieving a high final velocity during this type of movement. After a screening process of one hundred male participants, thirty-two were chosen to be further investigated who fell into the extremes of the strength and speed continuums. The main investigation involved having participants ballistically extend their elbows against external relative loads of 0%, 20%, 40%, 60% and 80% of their maximum isometric force and two absolute loads of 1.1 kg and 2.2 kg. External torque and angular displacement measurements were recorded as well as triceps and biceps electrical activity. EMG modeling, which employed the characteristics of muscle mechanics, was used to determine the differences in performance. Isometric strength did not produce a 1:1 mapping with maximum velocity. Individuals existed that were relatively strong but not fast. Additionally, there were subjects that were quite strong but not appreciably fast. Peak instantaneous power, however, produced the best correlations with peak final velocity. To determine why certain individuals were capable of producing more power, each subject's triceps EMG was modeled in order to predict the actual muscle torque. The model predicted torques with a mean correlation of 0.957 and a mean RMSerror value of 5.8 Nm for the 224 trials. As a result of the good predictions, a forward-dynamics approach was used to manipulate weaknesses in one performance with another individual's superior attributes. Performance improvements were noted as a result. These findings demonstrate that peak instantaneous power best predicts peak terminal velocity. Furthermore, this study has developed a model capable of identifying neuro-muscular weaknesses in performance and suggesting how improvements in those areas would change the maximum velocity attained. The next stage is to determine the proper training stimuli that would make these specific neuro-muscular improvements possible.

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