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Effect of eccentric exercise-induced muscle damage on the dynamics of muscle oxygenation and pulmonary oxygen uptake

¹School of Sport and Health Sciences, University of Exeter, St. Luke's Campus, Exeter, United Kingdom; ²Departments of Kinesiology, Anatomy and Physiology, Kansas State University, Manhattan, Kansas; and ³Department of Sport and Exercise Sciences, University of Chester, Chester, United Kingdom

Submitted 10 June 2008 ; accepted in final form 12 August 2008

Unaccustomed eccentric exercise has a profound impact on muscle structure and function. However, it is not known whether associated microvascular dysfunction disrupts the matching of O₂ delivery (O₂) to O₂ utilization (O₂). Near-infrared spectroscopy (NIRS) was used to test the hypothesis that eccentric exercise-induced muscle damage would elevate the muscle O₂:O₂ ratio during severe-intensity exercise while preserving the speed of the O₂ kinetics at exercise onset. Nine physically active men completed "step" tests to severe-intensity exercise from an unloaded baseline on a cycle ergometer before (Pre) and 48 h after (Post) eccentric exercise (100 squats with a load corresponding to 70% of body mass). NIRS and breath-by-breath pulmonary O₂ were measured continuously during the exercise tests and subsequently modeled using standard nonlinear regression techniques. There were no changes in phase II pulmonary O₂ kinetics following the onset of exercise (time constant: Pre, 25 ± 4 s; Post, 24 ± 2 s; amplitude: Pre, 2.36 ± 0.23 l/min; Post, 2.37 ± 0.23 l/min; all P > 0.05). However, the primary (Pre, 14 ± 3 s; Post, 19 ± 3 s) and overall (Pre, 16 ± 4 s; Post, 21 ± 4 s) mean response time of the [HHb] response was significantly slower following eccentric exercise (P < 0.05). The slower [HHb] kinetics observed following eccentric exercise is consistent with an increased O₂:O₂ ratio during transitions to severe-intensity exercise. We propose that unchanged primary phase O₂ kinetics are associated with an elevated O₂:O₂ ratio that preserves blood-myocyte O₂ flux.

near-infrared spectroscopy; oxygen uptake kinetics; muscle oxygen delivery; muscle oxygen utilization; delayed-onset muscle soreness

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