Training high living low: Changes of aerobic performance and muscle structure with training at simulated altitude

This study was undertaken to test the hypothesis that endurance training in hypoxia is superior to training of the same intensity in normoxia. To avoi d adaptation to hypoxia, the subjects lived under normoxic conditions when not training. A secondary objective of this study was to compare the effect of high-vs. moderate-intensity training on aerobic performance variables. Thirty-three men without prior endurance training underwent a cycle ergomet er training of 6 weeks, 5 d/week, 30 minutes/d. The subjects were assigned to 4 groups, N-high, N-low, H-high and H-low based on the training criteria normoxia (N; corresponding to a training altitude of 600 m), vs. hypoxia ( H; training altitude 3850 m) and intensity (high; corresponding to 80% and low: corresponding to 67% of (V) over dot O(2)max). (V) over dot O(2)max me asured in normoxia increased between 8.5 to 11.1%, independent of training altitude or intensity. (V) over dot O(2)max measured in hypoxia increased b etween 2.9 and 7.2%. Hypoxia training resulted in significantly larger incr eases than normoxia training. Maximal power that subjects could maintain ov er a thirty-minute period (measured in normoxia or hypoxia) increased from 12.3 - 26.8% independent of training altitude. However, subjects training a t high intensity increased performance more than subjects training at a low intensity. Muscle volume of the knee-extensors as measured by magnetic res onance imaging increased significantly in the H-high group only (+ 5.0%). M itochondrial volume density measured by EM-morphometry in biopsy samples of m. vastus lat. increased significantly in all groups with the highest incr ease seen in the H-high group (+ 59%). Capillary length density increased s ignificantly in the H-high group only (+ 17.2%). The main finding of this s tudy is that in previously untrained people, training in hypoxia while livi ng at low altitude increases performance in normoxia to the same extent as training in normoxia, but leads to larger increases of aerobic performance variables when measured under hypoxic conditions. Training intensity had no effect on the gain of (V) over dot O(2)max. On the level of skeletal muscl e tissue, the combination of hypoxia with high training intensity constitut es the most effective stimulus for increasing muscle oxidative capacity.