Reduced heterogeneity of muscle deoxygenation during heavy bicycle exercise.

PURPOSE This study evaluated heterogeneity of muscle O2 dynamics in a single muscle during bicycle exercise using an eight-channel near-infrared continuous wave spectroscopy (NIRcws) mapping system. METHODS Nine healthy subjects performed bicycle exercise at fixed workloads of 20, 40, 60, 80, and 100% maximal workload for 5 min at each level. Muscle oxygenation in the vastus lateralis (VL) during and after each exercise was monitored using the NIRcws mapping system. Pulmonary O2 uptake and heart rate were monitored continuously during the experiment. Blood samples were taken to measure blood lactate concentration at 30 s after each exercise stage. RESULTS Half time reoxygenation, the time taken to reach a value of half-maximal recovery, was significantly delayed in distal sites compared with proximal sites of VL. Conversely, muscle deoxygenation for all measurement sites increased incrementally with higher exercise workloads, and no significant difference of deoxygenation level showed within each channel. However, relative dispersion of muscle deoxygenation during exercise significantly decreased when the workload increased. Moreover, relative dispersion of muscle deoxygenation between the subjects also decreased with an increase in the workload. CONCLUSION Muscle deoxygenation in a single muscle was more heterogeneous at lower exercise workloads, and variations of the muscle deoxygenation heterogeneity between subjects were greater at lower exercise workloads.