Date of Award

2000

Degree Type

Thesis

Degree Name

Doctor of Philosophy

School

School of Biomechanical and Sports Science

Faculty

Faculty of Communications, Health and Science

First Advisor

Dr. Paul Sacco

Abstract

During many athletic events, fatigue influences the physiological and biomechanical characteristics of performance. For optimal performance in events such as rowing, athletes must maintain a skilfully co-ordinated movement technique. The ability to produce high force outputs during repetitive contractions is influenced by fatigue and dependent on a number of factors including neuromuscular activities. Neuromuscular activation may be expressed by amplitude and frequency characteristics of the electromyographic signal (EMG) sample from the muscle. During sustained isometric contractions, changes in EMG characteristics are related to changes in force, which may be useful in monitoring the fatigue process (Basmajian, 1974: De Luca, 1985). However, the force-EMG relationship is not as clear when applied lo dynamic contractions such as those in rowing performance. The central objective of this thesis is to assess the application of EMG in relation to biomechanical and physiological responses to rowing tasks. In particular, EMG characteristics of the quadriceps muscle in relation to total force output during a typical self-pace rowing ergometer performance. In order to reach the objective, five studies were undertaken in a systematic order. The studies had specific purposes, which included establishing force/torque-EMG relationships under controlled conditions and evaluating the transfer of force or torque output and EMG characteristics to less controlled performance conditions that were influenced by fatigue, pacing strategy, or both. In this investigation, trials (N – 117) were conducted on three ergometers affording varying levels of control over muscle length, contraction velocity, and muscle contribution to force output. Subjects (a – 11) that participated were selected from trained rowing crews. Trials were performed on an isokinetic dynamometer with analogue outputs of angular rotation and torque recorded. In addition, trials were performed on a leg-only ergometer and a standard rowing ergometer with performance outcomes recorded using a potentiometer to measure handle position and a strain gauge to measure force output. Bipolar surface electrodes were used to record EMC activity of the rectus femoris and vastus latcralis during all contractions. Biomechanical and EMO data were recorded on a data acquisition system (Amlab). Results validated the force/torque-rmsEMG relationship during non-fatiguing isometric, isokinetic, and dynamic contractions. During fatiguing contractions performed on the rowing ergometer, strength of the force/torquc-rmsEMG relationship was reduced and subject responses varied widely. Under the same condition, handle force and mean power frequency (MPF) of the vastus luteralis muscle showed a positive correlation. which might therefore be used to monitor fatigue during simulated rowing performance. EMG analysis was more appropriate when the exercise protocol was similar to that used during performance. Finally, a constant-pace strategy significantly reduced force loss and was associated with qualitative muscle activation changes that potentially might improve performance outcome. In conclusion, EMG analysis is constrained by methodological and confounding factors during dynamic exercise. Nevertheless EMG provides an insight into neural activation strategies during rowing fatigue and may be a useful tool for monitoring co-ordinated muscle activity and for devising strategies to improve performance.

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