Drift in Oxygen Consumption during Prolonged Sub-maximal Exercise in Subjects of Different Training Status

This study investigated whether the drift in oxygen consumption (VO2 drift) during prolonged cycling exercise at the lactate threshold (LT) is smaller in endurance-trained subjects than in sedentary subjects, and whether the change in muscle activity assessed using electromyography (EMG) during prolonged exercise is affected by training status and corresponds with VO2 drift. Seven sedentary (mean(SD), VO2max, 41.8(5.9) ml·kg·min−1) and eight endurance-trained men (VO2max, 58.7(5.4) ml·kg·min−1) performed prolonged cycling exercise for 70 min at the LT. During the prolonged exercises, VO2, VCO2, and the electrical activity of four muscles (vastus lateralis, vastus medialis, biceps femoris, and gastrocnemius medialis) were measured continuously. During 70 min exercise at the LT, the absolute VO2 drift in endurance-trained group was higher than sedentary group (469(189) ml vs 309(77) ml, respectively), whereas the relative VO2 drift was not differed between the sedentary and endurance-trained groups (1.20(0.04) times vs 1.21(0.08) times, respectively). Additionally, RMS and iEMG did not change during prolonged exercise. These results suggest that the relative VO2 drift during 70 min exercise at the LT was not differed between with the subject groups with the different training status and endurance capacity. The VO2 drift during 70 min exercise at the LT did not correspond with the changes in muscle activity of leg muscles, EMGs of which did not change throughout the experiments.