Four well-trained combination skiers were studied through pre- and post-training for the effects of short-term intermittent training during
hypoxia on muscle energetics during submaximal exercise as measured by
Phosphorus-31 nuclear magnetic resonance and maximal aerobic power (VO2max). The
hypoxia and training in the cold was conducted in a hypobaric chamber and comprised 60-min aerobic exercise (at an intensity equivalent to the blood
lactate threshold), using a cycle ergometer or a treadmill twice a day for 4, consecutive days at 5 degrees C, in conditions equivalent to an altitude of 2000 m (593 mm Hg). No change in VO2max was observed over the training period, while in the muscle energetics during submaximal exercise, the values of
phosphocreatine/(phosphocreatine+inorganic
phosphate) and intracellular pH were found to be significantly increased by training during
hypoxia. During recovery, the time constant of
phosphocreatine was found to have been significantly reduced [pre, 27.9 (SD 6.7) s; post, 22.5 (SD 4.7) s, P < 0.01]. The observed inhibition of
phosphocreatine as well as that of intracellular pH changes after training during
hypoxia and quicker recovery of
phosphocreatine in submaximal exercise tests, may indicate improved oxidative capacity (i.e. a high
adenosine 5'-
triphosphate formation rate) despite the short-term
hypoxia training.