Received December 3, 2004
Revised January 14, 2005
Accepted after revision January 26, 2005

¹ Kansas State University

^* To whom correspondence should be addressed. E-mail: tbarsto{at}ksu.edu.

	Abstract

In rat muscle, faster dynamics of microvascular PO₂ (~ blood flow-to-O₂ uptake ratio; Q_m/VO₂) after prior contractions that did not alter blood [lactate] have been considered to be a consequence of faster VO₂ kinetics. However, in humans, prior exercise below the lactate threshold does not affect the pulmonary VO₂ kinetics. To clarify this apparent discrepancy, we examined the effects of prior moderate exercise on the kinetics of muscle oxygenation (deoxyhemoglobin, [HHb] VO_2m/Q_m) and pulmonary VO₂ (VO_2p) in humans. Eight subjects performed two bouts (6 min each) of moderate-intensity cycling separated by 6 min of baseline pedaling. Muscle (vastus lateralis) oxygenation was evaluated by near-infrared spectroscopy and VO_2p was measured breath-by-breath. The time constant () of the primary component of VO_2p was not significantly affected by prior exercise (21.5 ± 9.2 vs. 25.6 ± 9.7 s; Bout 1 vs. 2, P = 0.49). The time delay (TD) of [HHb] decreased (11.6 ± 2.6 vs. 7.7 ± 1.5 s; Bout 1 vs. 2, P < 0.05) and [HHb] was longer (7.0 ± 3.5 vs. 10.2 ± 4.6 s; Bout 1 vs. 2, P < 0.05), while the mean response time (TD + ) did not change (18.6 ± 2.7 vs. 17.9 ± 3.9 s) after prior moderate exercise. Thus, prior moderate exercise resulted in shorter onset and slower rate of increase in [HHb] during subsequent exercise. These data suggest that prior exercise altered the dynamic interaction between VO_2m and Q_m following the onset of exercise.

Key Words: Exercise, Muscle, Oxygen

This article has been cited by other articles:

				B. Glancy, T. Barstow, and W. T. Willis Linear relation between time constant of oxygen uptake kinetics, total creatine, and mitochondrial content in vitro Am J Physiol Cell Physiol, January 1, 2008; 294(1): C79 - C87. [Abstract] [Full Text] [PDF]

				T. A. Bauer, J. E.B. Reusch, M. Levi, and J. G. Regensteiner Skeletal Muscle Deoxygenation After the Onset of Moderate Exercise Suggests Slowed Microvascular Blood Flow Kinetics in Type 2 Diabetes Diabetes Care, November 1, 2007; 30(11): 2880 - 2885. [Abstract] [Full Text] [PDF]

				A. J. Harper, L. F. Ferreira, B. J. Lutjemeier, D. K. Townsend, and T. J. Barstow Human femoral artery and estimated muscle capillary blood flow kinetics following the onset of exercise Exp Physiol, July 1, 2006; 91(4): 661 - 671. [Abstract] [Full Text] [PDF]

				S. L. Davis, P. J. Fadel, J. Cui, G. D. Thomas, and C. G. Crandall Skin blood flow influences near-infrared spectroscopy-derived measurements of tissue oxygenation during heat stress J Appl Physiol, January 1, 2006; 100(1): 221 - 224. [Abstract] [Full Text] [PDF]