Respiratory and locomotor muscle blood-volume and oxygenation kinetics during intense intermittent exercise

In this study, we examined the time course of changes in the blood volume and oxygenation of accessory respiratory (RM) and locomotor (LM) muscles, and the interrelationships of changes in these parameters during maximal incremental intermittent exercise in 15 non-endurance-trained active men. Blood volume and oxygenation of the serratus anterior and of vastus lateralis were measured simultaneously by near-infrared spectroscopy. The respiratory compensation point, and the breakpoints where abrupt changes were apparent in RM and LM blood volume and oxygenation versus time were identified. During exercise, the decreases in RM and LM oxygenation were accentuated in the vicinity of the respiratory compensation point. This was concomitant with a reduction in LM, but not RM, blood volume. The time at which the respiratory compensation point and the breakpoints in RM and LM blood volume and oxygenation were detected (70.2-75.0% exercise time) did not differ, and were inter-correlated (r=0.56 to 0.95). Moreover, the rate of the accelerated fall of oxygenation in the locomotor muscles was correlated with that of the decline in blood volume in that area (r=0.73), and with that of the accelerated fall of oxygenation in the respiratory muscles (r=0.71). The results suggest that the high ventilatory demand, which occurs naturally during intense intermittent exercise in non-endurance-trained individuals, may precipitate an accelerated fall in RM oxygenation, concomitant with a reduction in LM blood volume and an accentuated decline in LM oxygenation. Such responses are likely to occur above the respiratory compensation point during intermittent exercise.