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The Journal of Sports Medicine and Physical Fitness 2006 June;46(2):189-96

lingua: Inglese

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

Migita T. 1, 2, Hirakoba K. 2

1 Institute of Health and Sports Science Kurume University, Kurume, Japan
2 Division of Physiological and Biochemical Adaptation Graduate School of Life Science and System Engineering, Kyushu Institute of Technology, Kitakyushu, Japan


Aim. 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 (V.O2SC) during heavy constant-load exercise.
Methods. Two square-wave transitions of constant-load exercise were carried out at an exercise intensity corresponding to a V.O2 of 130% of the ventilatory threshold. The amplitude of the V.O2SC in phase III during heavy constant-load exercise was determined at normal (60 rpm) and extremely high pedal rates (110 rpm). The V.O2 kinetics were analyzed by nonlinear regression.
Results. Although the absolute work rates were almost identical in the two pedal rates cycling exercise, the amplitude of the V.O2 in phase II (phase II amplitude), end-exercise V.O2 (∆EEV.O2) 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 ∆EEV.O2; 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 V.O2SC 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 V.O2SC at 110 rpm, no corresponding changes in integrals of the electromyography (EMG) signal and mean power frequency were observed.
Conclusion. The results of this study indicate that the amplitude of the V.O2SC 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.

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