Influence of crank rate on the slow component of pulmonary O(2) uptake during heavy arm-crank exercise

The principal aim of this study was to examine the influence of variations in crank rate on the slow component of the pulmonary oxygen uptake ((.)VO(2)) response to heavy-intensity arm-crank ergometry (ACE). We hypothesized that, for the same external work rate, a higher crank rate would elicit a greater amplitude of the (.)VO(2) "slow component". Eleven healthy males (mean (+/- SD) age, 25 ((+/-6) y; body mass, 89.1 ((+/-10.7) kg; ACE (.)VO(2)(peak), 3.36 ((+/-0.47) L x min(-1)) volunteered to participate. The subjects initially completed an incremental exercise test for the determination of (.)VO(2)(peak) and peak power on an electrically braked arm ergometer. Subsequently, they completed "step" transitions from an unloaded baseline to a work rate requiring 70% of peak power: 2 at a crank rate of 50 r x min(-1) (LO) and 2 at a crank rate of 90 r x min(-1) (HI). Pulmonary gas exchange was measured on a breath-by-breath basis and (.)VO(2) kinetics were evaluated from the mean response to each condition using non-linear regression techniques. In contradiction to our hypothesis, the (.)VO(2) slow component was significantly greater at 50 r x min(-1) than at 90 r x min(-1) (LO: 0.60 +/- 0.30 vs. HI: 0.47 +/- 0.21 L x min(-1); p < 0.05). The mean value for the localized rating of perceived exertion was also higher at 50 r x min(-1) than at 90 r x min(-1) (LO: 16.7 +/- 1.4 vs. HI: 15.2 +/- 1.3; p < 0.05), but there was no significant difference in end-exercise blood lactate concentration. It is possible that differences in muscle tension development and blood flow resulted in a greater contribution of "low-efficiency" type II muscle fibres to force production at the lower crank rate in ACE, and that this was linked to the greater (.)VO(2) slow component. However, other factors such as greater isometric contraction of the muscles of the trunk and legs at the lower crank rate might also be implicated.