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Influence of priming exercise on pulmonary O₂ uptake kinetics during transitions to high-intensity exercise from an elevated baseline

¹School of Sport and Health Sciences, University of Exeter, Exeter, Devon; and ²Department of Sport and Exercise Science, Aberystwyth University, Ceredigion, United Kingdom

Submitted 4 March 2008 ; accepted in final form 23 May 2008

It has been suggested that the slower O₂ uptake (O₂) kinetics observed when exercise is initiated from an elevated baseline metabolic rate are linked to an impairment of muscle O₂ delivery. We hypothesized that "priming" exercise would significantly reduce the phase II time constant () during subsequent severe-intensity cycle exercise initiated from an elevated baseline metabolic rate. Seven healthy men completed exercise transitions to 70% of the difference between gas exchange threshold (GET) and peak O₂ from a moderate-intensity baseline (90% GET) on three occasions in each of the "unprimed" and "primed" conditions. Pulmonary gas exchange, heart rate, and the electromyogram of m. vastus lateralis were measured during all tests. The phase II O₂ kinetics were slower when severe exercise was initiated from a baseline of moderate exercise compared with unloaded pedaling (mean ± SD , 42 ± 15 vs. 33 ± 8 s; P < 0.05), but were not accelerated by priming exercise (42 ± 17 s; P > 0.05). The amplitude of the O₂ slow component and the change in electromyogram from minutes 2 to 6 were both significantly reduced following priming exercise (O₂ slow component: from 0.47 ± 0.09 to 0.27 ± 0.13 l/min; change in integrated electromyogram between 2 and 6 min: from 51 ± 35 to 26±43% of baseline; P < 0.05 for both comparisons). These results indicate that the slower phase II O₂ kinetics observed during transitions to severe exercise from an elevated baseline are not altered by priming exercise, but that the reduced O₂ slow component may be linked to changes in muscle fiber activation.

oxygen uptake kinetics; phase II time constant; oxygen uptake slow component; work-to-work transition