Uitslag, T. P., Galiart, R., Foster, C., Porcari, J. P., Daanen, H., Noordhof, D. A., & de Konig, J. J. (2010). Changes in gross efficiency during high intensity exercise. Presentation 2237 at the 2010 Annual Meeting of the American College of Sports Medicine, Baltimore, Maryland; June 2-5.

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This study evaluated the effect of ventilation and core temperature on gross mechanical efficiency before and after a time-trial exercise. Gross mechanical efficiency was measured during submaximal (50% POmax) exercise in trained cyclists (M = 11; F = 8) before and immediately after a four-minute time-trial (100% POmax), and during a control bout where the power output during the time-trial period remained at 50% POmax. Gas exchange was measured throughout the exercise bout and core temperature was measured using a radio pill.

Gross mechanical efficiency was reduced following the time-trial and had not recovered to control values within 10 minutes post-exercise. Change in gross mechanical efficiency was well correlated with the changes in ventilation (r = -.94), but not with changes in core temp (r = -.45). Gross mechanical efficiency decreased from ~18.0% at the beginning to ~15.5% at the end of the time-trial. This would result in a significant reduction in the aerobically attributable energy supply during the time-trial.

Implication. Gross mechanical efficiency decreases across the course of a four-minute high-intensity time-trial exercise. This suggests that gross mechanical efficiency measured before a time-trial (aerobic and anaerobic components) would not be represented in the actual time-trial. Because of the reduction in efficiency as fatigue accrues, athletes would do well to concentrate on technique features associated with efficiency to minimize the decrement.

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