Relationship Between Muscle Deoxygenation and Cardiac Output in Subjects Without Attenuation of Deoxygenation Hemoglobin Concentration Near the End of Ramp Cycling Exercise: A Longitudinal Study.

The aim of this study was to investigate the longitudinal relationship between the slopes of systemic and quadriceps muscle O dynamics in subjects without attenuation point in deoxygenated hemoglobin concentration at vastus lateralis (AP) during high-intensity cycling. Seven young men without AP performed ramp cycling exercise until exhaustion before and after 8 weeks, while continuing recreational physical activities throughout that period. Muscle O saturation (SmO) and deoxy-Hb were monitored at the vastus lateralis (VL) and rectus femoris (RF) by near infrared spectroscopy oximetry during exercise. Cardiac output (CO) was also continuously assessed. During high-intensity exercise, at VL, a significantly steeper slope of deoxy-Hb was found after 8 weeks compared with before, while the slopes of deoxy-Hb at RF were not significantly changed. Though a decrease in the slope of CO after 8 weeks did not reach significance (p = 0.12), the change in the slope of CO was significantly related to the change in the slopes of deoxy-Hb at VL (r = -0.89, p < 0.01) and RF (r = -0.86, p < 0.05). Our data reinforces the idea that, in subjects without AP, the slope of muscle deoxygenation at VL during high-intensity cycling exercise may partly be explained by systemic O supply, rather than O balance in other thigh muscles.