We developed a non-invasive measurement system for transient responses of oxygen delivery (Q) and consumption (VO₂) of active muscles. Further, effect of prior heavy exercise on spatial heterogeneity of muscle deoxygenation kinetics during subsequent heavy exercise was examined. Eight healthy men completed two 6-min bouts of cycling exercise at 80% of peak pulmonary VO₂, separated by 6 min of unloaded exercise. Pulmonary VO₂ was measured breath-by-breath, and the absolute concentration of deoxyhemoglobin/myoglobin (HHb) were assessed simultaneously at 4 different sites on the quadriceps muscle using multi-channel time-resolved near-infrared spectroscopy. Prior exercise had no effect on the time constant of the phase II pulmonary VO₂, but reduced the slow component of the bout 2. The amplitude of HHb was significantly larger at distal vastus lateralis muscle compared with other sites of the quadriceps. However, the kinetics of HHb was not different for all sites. Microvascular Q estimated from VO₂ and HHb was significantly higher in bout 2 compared with bout 1. In conclusion, it is suggested that muscle oxygen deliver for both bulk- and peripheral vascular sites are not limiting factor for muscle VO₂ kinetics at the onset of heavy exercise.

DESCENTE SPORTS SCIENCE Vol.30/THE DESCENTE AND ISHIMOTO MEMORIAL FOUNDATION FOR THE PROMOTION SPORTS SCIENCE