Ransom, V., Clark, A., vanLangen, F. A., Uitslag, T. P., Hettinga, F. J., De Koning, J. J., & Foster, C. (2008). Constant value of gross mechanical efficiency at high exercise intensity. ACSM 55th Annual Meeting Indianapolis, Presentation Number 802.

"Attribution of energetic sources during exercise depends on assuming gross efficiency is constant at high power output. Because of concerns regarding a VO2 slow component, gross efficiency is usually measured at intensities less than ventilatory threshold."

This study evaluated gross efficiency during steady state exercise relative to the VO2 at ventilatory threshold and peak power output to test the assumption of constant gross efficiency. Physically active Ss (N = 20) performed an incremental cycle exercise with stages of 3- or 6-minutes duration. Only stages with stable VO2 and a respiratory exchange ratio of less than 1.0 were included.

Gross efficiency increased with exercise intensity until the intensity associated with ventilatory threshold or 50% peak power output. It remained constant from then on through 160% ventilatory threshold and 75% peak power output.

Implication. Gross efficiency increases at low power output, probably because of a decreasing contribution from the baseline metabolic rate. However, at intensities significantly greater than ventilatory threshold, gross efficiency is constant. This finding supports the assumption that gross efficiency is unchanged during high intensity exercise and suggests the validity of attributing energy expenditure to aerobic and anaerobic sources.

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