Oxygenation Characteristics of the Vastus Lateralis During Cycling Exercise Performed Above Critical Power

Abstract

Near‐infrared spectroscopy has been used to empirically describe the oxygenation status of exercising skeletal muscle. Changes in total‐[Hb+Mb] and deoxy‐[Hb+Mb] concentrations have been thought to reflect changes in microvascular hematocrit (an index of diffusive conductance) and fractional oxygen extraction (an index of perfusive conductance), respectively. Our laboratory has previously shown that, following dynamic forearm exercise, no differences exist in the oxygenation status of the exercising muscle at task failure among exercise intensities performed above critical power (CP).PURPOSEThe purpose of this study was to investigate the oxygenation characteristics of the vastus lateralis muscle during cycling exercise performed at multiple intensities above critical power. We hypothesized that no significant differences would be detected in end‐exercise total‐[Hb+Mb] or deoxy‐[Hb+Mb] concentrations among exercise intensities.METHODSTo date, four healthy men (23.5 ± 2.0 yrs; 92.6 ± 4.2 kg; 175.2 ± 4.4 cm) performed an incremental exercise test on a cycle ergometer to determine peak power (Ppeak). Four constant load exercise tests were then performed to the limit of exercise tolerance (Tlim), from which CP was determined. Exercise intensities of the four constant load exercise tests were selected such that Tlim would occur between 2 and 15 minutes. Total‐[Hb+Mb] and deoxy‐[Hb+Mb] concentrations of the vastus lateralis were assessed using near‐infrared spectroscopy during each exercise bout.RESULTSCritical power (178 ± 17 W) was 59.4% ± 2.3% of Ppeak (300 ± 31 W). There was no significant overall effect of exercise intensity on end‐exercise total‐[Hb+Mb] concentration (p=0.26). While a significant overall effect of exercise intensity on end‐exercise deoxy‐[Hb+Mb] concentration was detected (p<0.05), there were no significant differences among exercise intensities. The end‐exercise total‐[Hb+Mb] (61.3 ± 16.1 μM) and deoxy‐[Hb+Mb] (23.0 ± 6.4 μM) concentrations were significantly correlated (r=0.96; p<.001).CONCLUSIONSThese preliminary data suggest that, following cycling exercise performed above critical power, the oxygenation status of the exercising muscle at task failure is not exercise intensity dependent. Further, these data suggest that perfusive (deoxy‐[Hb+Mb]) and diffusive (total‐[Hb+Mb]) conductances are associated at task failure.