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J Appl Physiol 95: 2014-2022, 2003. First published July 25, 2003; doi:10.1152/japplphysiol.00590.2002
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O2 uptake kinetics during exercise at peak O2 uptake

Barry W. Scheuermann1 and Thomas J. Barstow2

1Department of Health, Exercise and Sport Sciences, Texas Tech University, Lubbock, Texas 79409; and 2Department of Kinesiology, Kansas State University, Manhattan, Kansas 66506

Submitted 2 July 2002 ; accepted in final form 21 July 2003

Compared with moderate- and heavy-intensity exercise, the adjustment of O2 uptake (O2) to exercise intensities that elicit peak O2 has received relatively little attention. This study examined the O2 response of 21 young, healthy subjects (25 ± 6 yr; mean ± SD) during cycle ergometer exercise to step transitions in work rate (WR) corresponding to 90, 100, and 110% of the peak WR achieved during a preliminary ramp protocol (15-30 W/min). Gas exchange was measured breath by breath and interpolated to 1-s values. O2 kinetics were determined by use of a two- or three-component exponential model to isolate the time constant ({tau}2) as representative of O2 kinetics and the amplitude (Amp) of the primary fast component independent of the appearance of any O2 slow component. No difference in O2 kinetics was observed between WRs ({tau}90 = 24.7 ± 9.0; {tau}100 = 22.8 ± 6.7; {tau}110 = 21.5 ± 9.2 s, where subscripts denote percent of peak WR; P > 0.05); nor in a subgroup of eight subjects was {tau}2 different from the value for moderate-intensity (<lactate threshold) exercise ({tau}2 = 25 ± 12 s, P > 0.05). As expected, the Amp increased with increasing WRs (Amp90 = 2,089 ± 548; Amp100 = 2,165 ± 517; Amp110 = 2,225 ± 559 ml/min; Amp90 vs. Amp110, P < 0.05). However, the gain (G) of the O2 response ({Delta}O2/{Delta}WR) decreased with increasing WRs (G90 = 8.5 ± 0.6; G100 = 7.9 ± 0.6; G110 = 7.3 ± 0.6 ml·min-1·W-1; P < 0.05). The Amp of the primary component approximated 85, 88, and 89% of peak O2 during 90, 100, and 110% WR transitions, respectively. The results of the present study demonstrate that, compared with moderate- and heavy-intensity exercise, the gain of the O2 response (as {Delta}O2/{Delta}WR) is reduced for exercise transitions in the severe-intensity domain, but the approach to this gain is well described by a common time constant that is invariant across work intensities. The lower {Delta}O2/{Delta}WR may be due to an insufficient adjustment of the cardiovascular and/or pulmonary systems that determine O2 delivery to the exercising muscles or due to recruitment of motor units with lower oxidative capacity, after the onset of exercise in the severe-intensity domain.

maximal exercise; citrate synthase; fitness; efficiency; muscle fiber type


Address for reprint requests and other correspondence: B. W. Scheuermann, Dept. of Kinesiology, M.S. 201, The University of Toledo, Toledo, OH 43606 (E-mail: barry.scheuermann{at}utoledo.edu).




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