Muscle oxygenation after downhill walking-induced muscle damage

The purpose of this study was to investigate changes in muscle oxygenation and blood flow within vastus lateralis after an exhaustive session of downhill walking (DW). Nine healthy males performed 40-min DW on a treadmill with a gradient of -25% and at walking velocity of 6.4 km h(-1). To increase the likelihood that DW would induce muscle damage, subjects were loaded with 5% of their body weight carried in a back pack. Before and after DW exercise on day 1 and over the next 4 days, maximum voluntary contractions (MVCs), subjects' perception of muscle soreness (SOR), plasma creatine kinase (CK) activity and myoglobin (Mb) concentrations, and muscle oxygenation (using near infrared spectroscopy; NIRS) within vastus lateralis were assessed. Repeated-measures ANOVA revealed that MVC decreased while SOR and Mb concentration increase significantly (P<0.05) after DW, consistent with its effectiveness to evoke muscle damage. Resting tissue oxygen saturation increased immediately after DW, but recovered within 24 h. During isometric contractions at 30%, 50% and 80% of MVC, oxygen desaturation and re-saturation kinetics became significantly faster than pre-exercise values. The possible mechanism responsible for these changes might be increased resting muscle oxygen utilization after muscle damage because of an increased requirement for aerobic energy-demanding repair processes.