Leg Tourniquets Modify the On-Kinetics of Oxygen Uptake during Cycle Exercise

PURPOSE: Obstructive cardiovascular disease decelerates the on-kinetics of the body's oxygen uptake rate (VO₂), either by reducing the O ₂ delivery or by degrading the exercise capacity of skeletal muscle. This study sought to determine whether obstructed blood flow decelerates the on-kinetics of VO₂ by reducing O₂ delivery. METHODS: Breath-by-breath measurements of VO₂ were studied in eight healthy youth (age, 16.5 ± 0.6 years) during two-legged square-wave exercise on the cycle ergometer. The square protocol was 5 minutes of unloaded exercise followed by an immediate increase to 5 minutes of loaded exercise at 78 ± 5 W. In the experimental trials, thigh cuffs were inflated 30 seconds before the onset of loaded exercise. Control trials replicated the square-wave exercise with deflated thigh cuffs. RESULTS: The on-kinetics of VO₂ were biphasic in the control trial and triphasic in the experimental trial. Experimental VO₂ was significantly higher than control values in the final 90 seconds of exercise (P < .05). CONCLUSIONS: The difference between experimental and control VO₂ was attributable to inflated thigh cuffs. At no time was experimental VO₂ significantly lower than control VO₂. The clinical implication of the results is that skeletal myopathy, not reduced blood flow, is essential for decelerating the VO₂ on-kinetics of patients with obstructive vascular disease. The warranted conclusion is that square-wave exercise with inflated thigh cuffs stimulates a third phase of VO₂ on-kinetics.