Practice Effects On Muscle Activation (EMG), Metabolic Responses, and Coordination and Control Characteristics of a Novel Gross Motor Task

B. S. Lay & W. A. Sparrow

School of Health Sciences, Deakin University, Burwood, Australia


Previous studies of practice effects on motor skill acquisition have shown improvements in movement economy and associated changes in coordination and control variables. The aims of the experiment reported here were twofold: first to confirm earlier results and extend them by determining the effects of practice on muscle activation (EMG). Second to employ pre- and post-test sub-maximal oxygen consumption tests to confirm that practice-related changes in metabolic variables cannot be attributed to improvements in cardiovascular efficiency. Six healthy well-trained male volunteers with no experience of rowing undertook one 16 minute practice session per day for 10 days on a rowing ergometer at fixed power output (100 Watts) and preferred stroke rate. Oxygen consumption and perceived exertion (central and peripheral) declined significantly with practice. Stroke rate decreased significantly with practice consistent with a shift to a "longer-slower" coordination mode observed in previous studies. Peak force applied to the ergometer handle was significantly less variable following practice, while the mean and the standard deviation of the impulse produced per stroke both reduced with practice. Improved stability of response was also evident in (post-practice) more tightly clustered phase-plane (velocity/displacement) plots for the hip.

The most important finding was that IEMG of both the vastus lateralis and the biceps brachii revealed a decrease following practice. Interestingly, one participant demonstrated a shift in activation from the arms to the legs that may be indicative of a search for a more economical coordination and control profile. In addition, improved economy was found with no significant changes in predicted peak pre- (54.01 + 8.2 to post-test (56.35 + 9.88 The results here are interpreted as providing support for the view that humans are sensitive to the metabolic cost of exercise and that practice-related refinements to coordination and control are constrained by the propensity to reduce metabolic energy expenditure.