Effect of internal power on muscular efficiency during cycling exercise

The purpose of this study was to investigate the muscular efficiency during cycling exercise under certain total power output (Ptot) or external power output (Pext) experimental conditions that required a large range of pedal rates from 40 to 120 rpm. Muscular efficiency estimated as a ratio of Ptot, which is sum of internal power output (Pint) and Pext, to rate of energy expenditure above a resting level was investigated in two experiments that featured different conditions on a cycle ergometer, which were carried out at the same levels of Ptot (Exp. 1) and Pext (Exp. 2). Each experiment consisted of three exercise tests with three levels of pedal rates (40, 80 and 120 rpm) lasting for 2-3 min of unloaded cycling followed by 4-5 min of loaded cycling. VO2 during unloaded cycling (approximately 430 ml min(-1) for 40 rpm, approximately 640 ml min(-1) for 80 rpm, approximately 1,600 ml min(-1) for 120 rpm) and the Pint (approximately 3 W for 40 rpm, approximately 25 W for 80 rpm, approximately 90 W for 120 rpm) in the two experiments were markedly increased with increasing pedal rates. The highest muscular efficiency was found at 80 rpm in the two experiments, whereas a remarkable reduction (19%) in muscular efficiency obtained at 120 rpm could be attributable to greater O2 cost due to higher levels of Pint accompanying the increased pedal rates. We concluded that muscular efficiency could be affected by the differences in O2 cost and Pint during cycling under the large range of pedal rates employed in this study.