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 (P _tot) or external power output (P _ext) experimental conditions that required a large range of pedal rates from 40 to 120 rpm. Muscular efficiency estimated as a ratio of P _tot, which is sum of internal power output (P _int) and P _ext, 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 P _tot (Exp. 1) and P _ext (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. \( \dot V{\text{O}}_2 \) during unloaded cycling (∼430 ml min⁻¹ for 40 rpm, ∼640 ml min⁻¹ for 80 rpm, ∼1,600 ml min⁻¹ for 120 rpm) and the P _int (∼3 W for 40 rpm, ∼25 W for 80 rpm, ∼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 P _int accompanying the increased pedal rates. We concluded that muscular efficiency could be affected by the differences in O₂ cost and P _int during cycling under the large range of pedal rates employed in this study.