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

Purpose: To examine the relationship between muscle oxygenation and arterio venous oxygen difference [(a - (v) over bar)O-2diff)] at four constant rate workloads in healthy men and women and to compare these responses between the genders, Methods: Nineteen men and 14 women consented to perform an inc remental test to identify the lactic acidosis threshold (LAT) and maximal a erobic power ((V) over dot O-2max) and an intermittent constant work rate t est at an oxygen uptake corresponding to 40% LAT, 80% LAT, 25% LAT-(V) over dot O-2max, and 50% LAT-(V) over dot O-2max. 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) over bar)O-2diff was compu ted. Tissue absorbency was measured from the vastus lateralis in both the t est sessions using near infrared spectroscopy (NIRS). Muscle oxygenation du ring constant work rate exercise and recovery was expressed as a percentage (%Mox) of the maximum range observed during incremental exercise and recov ery. Results: A systematic decrease was observed in %Mox with increasing in tensity, followed by a proportional increase during recovery from each exer cise bout. Significant inverse relationships were observed between %Mox and (a - (v) over bar)O-2diff in men (r = -0.34) and women (r = -0.31) across the four intensities. Mean %Mox was significantly higher (P < 0.05) in wome n compared with men, suggesting lesser deoxygenation at the same relative e xercise intensity. Conclusions: %Mox was not an accurate predictor of mixed (a - (v) over bar)O-2diff during exercise because of the low common varian ce between these two variables, and it is unclear whether the gender differ ence in %Mox is a true physiological phenomenon or whether it is an artifac t of the NIPS technique.