Physiological Contributors to the Slow Component of Oxygen Uptake Kinetics during High Intensity Cycling Exercise

Abstract

0102 The mechanisms of the slow component of oxygen uptake kinetics have not been definitively established. Some studies have shown the source of extra oxygen cost of constant-load exercise above the lactate threshold resides within the exercising limbs. PURPOSE: The purpose of this study was to evaluate the slow component as a function of changes in muscle activity, lactate accumulation in the blood, ventilation, heart rate and stroke volume. METHODS: Forty-five participants (34 males, 11 females), reported to the lab on two separate days. On the first day, a maximal exercise test to exhaustion was performed on a cycle ergometer with gas exchange measurements. A high intensity exercise level was established by taking 60% of the difference between ventilatory threshold and VO2peak. Following a 5-minute warm-up at a low intensity, 15 minutes of high intensity exercise was performed. Gas exchange data, muscle RMS EMG, lactate and Doppler data were collected. RESULTS: A significant slow component of VO2 was achieved with a magnitude of 233.92 ± 180.37 mL from minute 3 of exercise to the end. There was very little change in muscle activity of the vastus lateralis (ΔVL, 0.58 × 10−2 mV), vastus medialis (ΔVMO, −0.33 × 10−2 mV), rectus femoris (ΔRF, 0.01 × 10−2 mV), biceps femoris (ΔBF, 0.07 × 10−2 mV), tibialis anterior (ΔTA, 1.44 × 10−2 mV) and gastrocnemius (ΔGAS, 0.30 × 10−2). Lactate values increased significantly (ΔLA, 3.66 ± 2.97 mmol), as did ventilation (ΔVE, 27.65 ± 16.43 L/min). Though velocity time integral increased slightly, this change was not significant (ΔVTI, 0.38 ± 4.4 cm) while heart rate increased significantly from minute 3 to end of exercise (ΔHR, 18 ± 6 bpm). When these variables were included in a blocked regression model, ventilation was the only consistent predictor of the VO2 slow component, p ≤ 0.05. Lactate, RMS EMG, VTI and HR did not contribute. CONCLUSIONS: Only the change in ventilation was a significant predictor of the slow component. Change in muscle EMG activity and muscle recruitment was unrelated to the slow component, as was changes in blood lactate and heart rate.