The decline in gross efficiency in relation to cycling time-trial length

To evaluate whether gross efficiency (GE), determined during submaximal cycling, is lower after time trials and if the magnitude of the decrease differs in relation to race distance. Secondary purposes were to study the rate of the decline in GE and whether changes in muscle-fiber recruitment could explain the decline.

Cyclists completed 9 GE tests consisting of submaximal exercise performed before and after time trials of different length (500 m, 1000 m, 2000 m, 4000 m, 15,000 m, and 40,000 m). In addition, subjects performed time trials as if they were a 1000-m, 4000-m, or 40,000-m time trial during which they were stopped at 50% of the final time of the preceding "full" time trial. Power output, gas exchange, and EMG were measured continuously throughout the GE tests.

A significant interaction effect between distance and time was found for GE (P = .001). GE was significantly lower immediately after the time trials than before (P < .05), and the decline in GE differed between distances (P < .001). GE seemed to decline linearly during the relatively short trials, while it declined more hyperbolically during the 40,000-m. A significant effect of time (P = .04) on mean EMG amplitude was found. However, post hoc comparisons showed no significant differences in mean EMG amplitude between the different time points (before and after the time trials).

GE decreases during time-trial exercise. Unfortunately, the cause of the decrease remains uncertain. Future modeling studies should consider using a declining instead of a constant GE. In sport situations, the declining GE has to be taken into account when selecting a pacing strategy.