Systemic and Quadriceps Muscle O2 Dynamics in Subjects Without Attenuation Point of Deoxygenated Haemoglobin Concentration During Ramp Cycling Exercise

The aim of this study was to compare systemic and quadriceps muscle O2 dynamics between aerobic capacity-matched subjects without (NAP; n = 5) and with (CON; n = 13) attenuation point in deoxygenated haemoglobin concentration (deoxy-Hb) at vastus lateralis (APdeoxy-Hb@VL) during ramp cycling exercise. Muscle O2 saturation (SmO2) and deoxy-Hb were monitored at the vastus lateralis (VL), rectus femoris (RF), and vastus medialis (VM) by spatial resolved near infrared spectroscopy during exercise. Cardiac output (CO) and pulmonary O2 uptake (VO2) were also continuously measured. During high-intensity exercise, in NAP, steeper slopes of both deoxy-Hb and SmO2 were found at VM, similar to VL muscle. Additionally, at RF, the slope of deoxy-Hb was steeper in NAP than CON. While the slope of pulmonary VO2 was similar between groups, the slope of CO was shallower in NAP than CON. During moderate intensity exercise, the slopes of all variables were similar between groups. These results suggest that the slope of muscle deoxygenation was enhanced not only in VL but also other thigh muscles in NAP, compared to CON. Because the slope of CO was associated with the slope of SmO2 and deoxy-Hb at VL during high-intensity exercise, the differences in subjects with and without APdeoxy-Hb@VL may be partly explained by systemic O2 supply, rather than O2 balance in the other quadriceps muscles.