Losa-Reyna, J., Ponce-Gonzalez, J. G., de Torres-Peralta, R. S., Perez, Suarez, I., Feijoo, D., Martinez-Munoz, P. J., Rodriguez-Garcia, L., Calle-Herrero, J., & Calbet, J. A. (2012). The ergogenic effect of oxygenation at exhaustion in severe acute hypoxia: A placebo effect? Presentation 2156 at the 59th Annual Meeting of the American College of Sports Medicine, San Francisco, California; May 29-June 2, 2012.

This study determined the minimal level of oxygenation required to swiftly relieve fatigue in hypoxic exercised humans. Males (N = 10) performed five randomized incremental exercise tests (cycle ergometer, 80 rpm) to exhaustion on different days. One test was carried out in normoxia (Nx; increasing 30 watts every two minutes). The other four tests started in severe hypoxia (PIO2=74 mmHg; increasing 20 watts every two minutes) (HYP1). At exhaustion (inability to maintain a pedaling rate above 50 rpm despite strong verbal encouragement for 5 seconds) the breathing gas mixture was swiftly changed and Ss requested to try to overcome fatigue. After two minutes the intensity was increased (increasing 20 watts every two minutes) until exhaustion (HYP2). Four different gas mixtures were randomly administered in HYP2 (PIO2= 74 (placebo), 83, 91, 99 mmHg). At exhaustion, Ss were again requested to overcome fatigue when swiftly switched to breathe normoxia (NX3, increasing 20 watts every two minutes) and after two minutes the exercise intensity was increased (increasing 20 watts every two minutes) until termination.

Similar VO2max vales were achieved in NX3 and in the control incremental test in Nx . The transition to HYP2 resulted in significantly increased work only for the 99 mmHg PIO2. A placebo effect accounted for 25% of the extra work performed with oxygenation in HYP2. The transition to NX3 allowed continuing the incremental exercise in all conditions. The work performed in NX3 was significantly lower when the preceding PIO2 was 99 mmHg compared to the other conditions.

Implication. Fatigue during incremental exercise to exhaustion in severe acute hypoxia is swiftly relieved by even small increases in oxygenation. The latter combined with the existence of a placebo effect is compatible with central fatigue as the main mechanism causing exhaustion during exercise in either moderate or severe acute hypoxia.

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