OXYGEN DELIVERY IS NOT A LIMITING FACTOR IN INTENSE EXERCISE IN NORMOXIA
Christensen, P. M., Nordsborg, N., Nybo, L., Secher, N., Sander, M., & Bangsbo, J. (2012). Moderate hypoxia does not slow muscular oxygen uptake at the onset of intense exercise. Presentation 2213 at the 59th Annual Meeting of the American College of Sports Medicine, San Francisco, California; May 29-June 2, 2012.
This study investigated if a reduction in oxygen delivery through the inspiration of hypoxic gas causes lower oxygen uptake of the contracting muscles during intense exercise. Healthy young males (N = 6) performed an intense 2-legged knee-extensor exercise for two minutes in hypoxia (13% oxygen) and normoxia on separate days. Catheters were placed in the femoral artery and vein allowing for blood samples and blood flow measurements at rest, just prior to exercise, and after 3, 6, 9, 12, 15, 20, 40, 60 and 120 seconds of exercise.
Blood flow was similar in both conditions. However, arterial oxygen content was lowered from normia to hypoxia, resulting in a ~20-30% reduction in oxygen delivery in the hypoxic condition. The arterial-venous oxygen difference was similar between conditions. Thus, muscular oxygen uptake was not affected by the reduced oxygen delivery. Lactate release and pH were similar between conditions.
Implication. The present study shows that muscular oxygen uptake and anaerobic lactic metabolism during intense two-legged knee-extensor exercise is unaffected despite a 20-30% reduction in oxygen delivery caused by inspiring hypoxic air. It is suggested that oxygen delivery in normoxia does not limit muscle oxygen uptake during intense exercise.
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