Kinetics of oxygen uptake at the onset of exercise in boys and men

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Abstract
The objective of this study was to compare the O2 uptake (V˙o2) kinetics at the onset of heavy exercise in boys and men. Nine boys, aged 9–12 yr, and 8 men, aged 19–27 yr, performed a continuous incremental cycling task to determine peak V˙o2(V˙o2 peak). On 2 other days, subjects performed each day four cycling tasks at 80 rpm, each consisting of 2 min of unloaded cycling followed twice by cycling at 50%V˙o2 peak for 3.5 min, once by cycling at 100%V˙o2 peak for 2 min, and once by cycling at 130%V˙o2 peak for 75 s. O2 deficit was not significantly different between boys and men (respectively, 50%V˙o2 peak task: 6.6 ± 11.1 vs. 5.5 ± 7.3 ml ⋅ min−1 ⋅ kg−1; 100% V˙o2 peak task: 28.5 ± 8.1 vs. 31.8 ± 6.3 ml ⋅ min−1 ⋅ kg−1; and 130%V˙o2 peaktask: 30.1 ± 5.7 vs. 35.8 ± 5.3 ml ⋅ min−1 ⋅ kg−1). To assess the kinetics, phase I was excluded from analysis. Phase IIV˙o2 kinetics could be described in all cases by a monoexponential function. ANOVA revealed no differences in time constants between boys and men (respectively, 50%V˙o2 peaktask: 22.8 ± 5.1 vs. 26.4 ± 4.1 s; 100%V˙o2 peak task: 28.0 ± 6.0 vs. 28.1 ± 4.4 s; and 130%V˙o2 peak task: 19.8 ± 4.1 vs. 20.7 ± 5.7 s). In conclusion, O2 deficit and fast-componentV˙o2 on-transients are similar in boys and men, even at high exercise intensities, which is in contrast to the findings of other studies employing simpler methods of analysis. The previous interpretation that children rely less on nonoxidative energy pathways at the onset of heavy exercise is not supported by our findings.