Effect of different pedal rates on oxygen uptake slow component during constant-load cycling exercise

We hypothesized that an extremely high pedal rate would induce much more type II muscle fibers recruitment even at an early phase of the same absolute work rate compared with normal pedal rates, and would result in changed amplitude of the pulmonary oxygen uptake slow component (VO(2)SC) during heavy constant-load exercise.

Two square-wave transitions of constant-load exercise were carried out at an exercise intensity corresponding to a VO(2) of 130% of the ventilatory threshold. The amplitude of the VO(2)SC in phase III during heavy constant-load exercise was determined at normal (60 rpm) and extremely high pedal rates (110 rpm). The VO(2) kinetics were analyzed by nonlinear regression.

Although the absolute work rates were almost identical in the two pedal rates cycling exercise, the amplitude of the VO(2) in phase II (phase II amplitude), end-exercise VO(2) (EEVO(2)) and blood lactate accumulation ([La]) were significantly greater at 110 rpm than at 60 rpm (2 260+/-242 vs 1.830+/-304 mL.min(-1) for phase II amplitude; P<0.01, 2 350+/-265 vs 1 709+/-342 mL.min(-1) for EEVO(2); P<0.01, 6.4+/-1.3 vs 3.2+/-1.3 mmol.L(-1) for [La]; P<0.01, respectively). The amplitude of the VO(2)SC in phase III also revealed a significantly higher value at 110 rpm compared with 60 rpm (416+/-73 vs 201+/-89 mL.min(-1), P<0.01). In spite of the appearance of greater VO(2)SC at 110 rpm, no corresponding changes in integrals of the electromyography (EMG) signal and mean power frequency were observed.

The results of this study indicate that the amplitude of the VO(2)SC was greater in higher pedal rate during the same work rate constant-load cycling exercise, which might be associated with a progressive increase in the adenosine triphosphate requirement of already recruited muscle fibers in exercising muscle.