2-1 VO2 and Muscle Oxygenation Kinetics during Sinusoidal Walking Exercise in Humans

We observed the O2 uptake (VO2) and deoxygenation (HHb) kinetics in 13 healthy subjects to sinusoidal walking between 3 km/h and 6 km/h on a treadmill. Tests were performed at sinusoidal periods of 10, 5, 2, and I min and in steady-state. When the periods of speed oscillations decreased, the amplitude of VO2 oscillations decreased sharply and the phase shift between VO2 and treadmill speed oscillations increased. Phase shift in VO2 during sinusoidal walking was significantly smaller than during sinusoidal cycling when metabolic demand was similar. Phase shift in a capillary blood flow (Qcap) calculating as VO2/HHb tended to be larger than VO2, and a faster HHb kinetics was observed compared to VO2 and Qcap kinetics. These results suggest that VO2 kinetics during sinusoidal walking was attributed to efficient muscle oxidative machinery as the limiting factor.