Muscle oxidative capacity does not appear to influence NIRS-VOT outcomes in healthy adults

Near-infrared spectroscopy (NIRS) with vascular occlusion testing (VOT) is used to assess skeletal muscle tissue oxygenation (StO₂) responses. Differences in NIRS-VOT outcomes exist between trained and untrained groups; however, it is unclear whether muscle oxidative capacity is a primary determinant of these differences. Our purpose was to test whether NIRS-VOT outcomes differ between adults with relatively high versus low muscle oxidative capacity, and whether desaturation rates correlate with post-exercise recovery kinetics of muscle oxygen consumption (mV̇O₂).

Twenty-five adults (12 women) completed assessments of whole-body maximal oxygen uptake (V̇O_2max) and vastus lateralis oxidative capacity, as well as a NIRS-VOT. The NIRS-VOT outcomes included downslope, upslope, and maximum StO₂ (StO_2max). Muscle oxidative capacity (rate constant, k) was quantified following a cycling bout at 50% of peak power at V̇O_2max. Participants were divided into two groups based on k values. Independent t-tests and Bayesian estimation were used to compare NIRS-VOT outcomes between the groups. Pearson's correlation coefficient examined the relation between downslope and k.

As expected, the high muscle oxidative capacity group showed greater muscle oxidative capacity than the low group (p < 0.01). Independent t-tests revealed no significant (p > 0.05) differences between groups for downslope, upslope, or StO_2max. Bayesian analyses supported these findings. No significant (p > 0.05) correlations were found between downslope and k across the total sample or subgroups.

Contrary to our hypothesis, muscle oxidative capacity did not appear to yield group differences in NIRS-VOT outcomes. Furthermore, the resting rate of desaturation is unlikely to be a valid indicator of muscle oxidative capacity.