Noordhof, D. A., Mulder, R. C., Malterer, K. R., Foster, C., & de Konig, J. J. (2013). Changes in gross efficiency in relation to time-trial length. Medicine & Science in Sports & Exercise, 45(5), Supplement abstract number 602.

This study evaluated if gross efficiency, determined during submaximal exercise, is lower after time-trial exercise and if the magnitude of the decrease in gross efficiency differed between time-trial lengths. Secondary purposes were to study the rate of the decline in gross efficiency and if muscle fiber recruitment caused a decrement in gross efficiency. Well-trained cyclists (N = 19) completed nine gross efficiency tests, consisting of submaximal cycling, at 65% of the power output performed before and after different time-trials (500 m, 1,000 m, 2,000 m, 4,000 m, 15,000 m, 40,000 m, 1,000 m split, 4,000 m split, 40,000 m split). During the split-trials, Ss were stopped after half the time of the corresponding time-trial and then continued with the gross efficiency test. Gas exchange and EMG were recorded during all tests. Gross efficiency was determined during the submaximal bouts before and after the time-trial and was estimated at the end of the (split) time-trial using back-extrapolation.

A significant effect of time (pre, extrap, post1, post2) and a significant interaction between distance and time on gross efficiency was determined. Gross efficiency was significantly lower after the time-trials and the magnitude of the decrement in gross efficiency was larger for shorter trials. The rate of the decline in gross efficiency seemed constant for short time-trials, but by half time in the 40,000 m the ultimate decrement in gross efficiency was almost attained. A significant effect of time (pre, post1, post2) and muscle was found on EMG amplitude. There was no significant difference in EMG amplitude between the different time points.

Implication. Gross efficiency was lower after time-trial exercise and the decrement in gross efficiency was larger for short time-trials. The decrement cannot be explained by a change in muscle fiber recruitment.

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