DIFFERENCE IN OXYGEN SUPPLY—CONSUMPTION BALANCE IN THIGH MUSCLES WORKING TOGETHER DURING KNEE—EXTENSION EXERCISE

Abstract

The purpose of this study was to clarify the changes in oxygen kinetics in two different thigh muscles recruited for dynamic knee-extension exercise at varying intensities in seven female subjects. Pulmonary oxygen uptake (Vo₂) was measured by the 10-s mixing chamber method. Changes in oxygenated hemoglobin (HbO₂), deoxygenated hemoglobin (Hb), and total hemoglobin (HbT) contents were measured in the vastus lateralis (VL) and rectus lemons (RF) muscles using near-infrared spectroscopy, and the oxygen saturation (SO₂) was calculated as the HbO₂ divided by HbT in percent. The surface electromyograms (EMG) of both muscles were also recorded. The integrated EMGs (iEMG) of the VL and RF increased linearly with increasing exercise intensity up to 100%VO_2peak. However, the HbO₂ and Hb remained unchanged when exercise intensity was below 50%Vo_2peak, above which the increase in Hb and decrease in HbO₂ were observed. Thus the decline in SO₂ occurred at 60%Vo_2peak in the RF, and 70%Vo_2peak in the VL. These results suggest that muscle deoxygenation is accelerated during exercise above a certain intensity, which is lower in the RF than in the VL, during dynamic knee-extension exercise.