Roels, B., Bentley, D. J., Coste, O., Mercier, J., & Millet, G. P. (2006). Effects of intermittent hypoxic training on altitude and sea-level cycling performance in well-trained athletes. Medicine and Science in Sports and Exercise, 38(5), Supplement abstract 908.

"Intermittent hypoxic training (IHT) is based on the assumption that brief exposures to hypoxia (minutes to hours) are sufficient to stimulate the release of EPO, and ultimately increase the red blood cell concentration. However, data investigating the effects of IHT on hematological variables and endurance performance are inconclusive and rather minimal".

Endurance athletes were divided into a normoxic (N = 9) and an intermittent hypoxic training group (N = 10) and completed a three-week training program (5 x 1-1.5 hours per week). The training sessions were under normoxic and then hypoxic conditions (simulated altitude of ~3000 m). Blood samples at rest were obtained before, during, and after the training program. Three incremental cycling tests to exhaustion as well as a 10-minute time trial were performed before and after the experimental period.

Intermittent training performed in hypoxia (simulated altitude) was less efficient than similar training in normoxia in terms of endurance performance measured in normoxia. Intermittent hypoxic and normoxic exercise training increased peak power output at sea-level to the same extent. Intermittent hypoxic training increased peak power output in simulated altitude conditions. The different exercise training conditions did not induce any changes in VO2max or in hematological variables.

Implication. Five sessions per week of three weeks of exercise training significantly improved normoxic peak power output and cycling time-trial performance. Performing similar training under intermittent hypoxic conditions failed to enhance those improvements. To the contrary, endurance performance measured in normoxia was unchanged after simulated altitude training, whereas it was improved after the sea-level training. Therefore, the primary purpose of hypoxic training -- to enhance sea-level performance more than normal training -- was invalidated.

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