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

Abstract

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.