[Altitude training--what is true?]

Because of the importance of oxygen transport and consumption in the body for endurance performance altitude training as preparation for competitions at sea level has come into use. In hypoxia maximal O2 uptake decreases. Thus for equal work load training at altitude is harder and stimulates adaptation processes more than sea level training. A specific altitude training effect, however, can only be proven if a relative equal load (in % of VO2max) is more effective than during sea level training. In only 3 of 10 investigations with this design a significant improvement of either maximal performance, VO2max or endurance was found, in 2 there was a nonsignificant tendency. When training in hypoxia combined with living in normoxia was investigated two of four groups improved. Presumably there exists a small specific altitude effect on performance capacity, which may be counteracted by negative influences like reduced muscular metabolic intensity. A series of single physiological changes at altitude might have positive or negative influences on training success: training of ventilatory muscles, increase of hypoxic ventilatory stimulation, reduced heart training by vegetative 'braking', increase of red cell and plasma volume (the latter after descent), right shift of the oxygen dissociation curve, increase of oxidative muscle enzymes (only after hypoxia training), shift from carbohydrate to fat combustion, reduced lactic acid and ammonia production, improvement of buffering.