The purpose of this study was to examine how oxygen uptake (V . o2) in decrement-load exercise (DLE) is affected by changing rate of decrease in power output. DLE was performed at three different rates of decrease in power output (10, 20 and 30 watts·min-1: DLE10, DLE20 and DLE30, respectively) from power output corresponding to 90 % of peak V . o2. V . o2 exponentially increased and then decreased, and the rate of its decrease was reduced at low power output. The values of V . o2 in the three DLE tests were not different for the first 2 min despite the difference in power output. The relationship between V . o2 and power output below 50 watts was obtained as a slope to estimate excessive V . o2 (ex-V . o2) above 50 watts. The slopes were 10.0±0.9 for DLE10, 9.9±0.7 for DLE20 and 10.2±1.0 ml·min-1·watt-1 for DLE30. The difference between V . o2 estimated from the slope and measured V . o2 was defined as ex-V . o2. The peak value of ex-V . o2 for DLE10 (189±116 ml·min-1) was significantly greater than those for DLE20 and for DLE30 (93±97 and 88±34 ml·min-1). The difference between V . o2 in DLE and that in incremental-load exercise (ILE) below 50 watts (?V . o2) was greater in DLE30 and smallest in DLE10. There were significant differences in ?V . o2 among the three DLE tests. The values of ?V . o2 at 30 watts were 283±152 for DLE10, 413±136 for DLE20 and 483±187 ml·min-1 for DLE30. Thus, a faster rate of decrease in power output resulted in no change of V . o2 at the onset of DLE, smaller ex-V . o2 and greater ?V . o2. These results suggest that V . o2 is disposed in parallel in each motor unit released from power output or recruited in DLE.

Laboratory of Exercise Physiology Graduate School of Education Hokkaido University Sapporo

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