Muscle oxygenation trends during constant work rate cycle exercise in men and women

To examine the relationship between muscle oxygenation and arteriovenous oxygen difference [(a - v)O2diff)] at four constant rate workloads in healthy men and women and to compare these responses between the genders.

Nineteen men and 14 women consented to perform an incremental test to identify the lactic acidosis threshold (LAT) and maximal aerobic power (VO2max) and an intermittent constant work rate test at an oxygen uptake corresponding to 40% LAT, 80% LAT, 25% LAT-VO2max, and 50% LAT-VO2max. Each exercise interval was 5 min long followed by 2 min of recovery. Cardiac output was measured by CO2 rebreathing at each workload from which (a - v)O2diff was computed. Tissue absorbency was measured from the vastus lateralis in both the test sessions using near infrared spectroscopy (NIRS). Muscle oxygenation during constant work rate exercise and recovery was expressed as a percentage (%Mox) of the maximum range observed during incremental exercise and recovery.

A systematic decrease was observed in %Mox with increasing intensity, followed by a proportional increase during recovery from each exercise bout. Significant inverse relationships were observed between %Mox and (a - v)O2diff in men (r = -0.34) and women (r = -0.31) across the four intensities. Mean %Mox was significantly higher (P < 0.05) in women compared with men, suggesting lesser deoxygenation at the same relative exercise intensity.

%Mox was not an accurate predictor of mixed (a - v)O2diff during exercise because of the low common variance between these two variables, and it is unclear whether the gender difference in %Mox is a true physiological phenomenon or whether it is an artifact of the NIRS technique.