Abstract
The effects of prolonged severe hypoxia on human performance capacity and muscle structure
and function have recently been studied during real and simulated ascents to Mt. Everest.
The results of several independent research teams, using different techniques, are
broadly compatible. It is found that body and muscle mass is significantly reduced
after exposure to hypoxia. As a consequence, muscle fiber size is also reduced. The
capillary density of muscle tissue is increased, not because of capillary neoformation,
but because of the reduction in muscle fiber size The activities of enzymes of the
oxidative pathways are decreased in skeletal muscle tissue. A loss of mitochondria
is the structural evidence of the diminished potential for muscle oxidative metabolism.
In contrast to these results, recent experimentations with hypoxia in human exercise
settings have demonstrated that if hypoxia is only present during a limited daily
period of an endurance training session, hypoxia has a different effect on muscle
tissue. It is found that muscle fiber size, capillarity, myoglobin concentration and
muscle oxidative capacity are all enhanced with training in hypoxia. These controversial
findings raise questions regarding the nature of the adaptational mechanisms triggered
by the different hypoxic stimuli to which subjects had been subjected and thus offer
important new venues for further studies on the control of protein metabolism in muscle
tissue.
Key words
Human - hypoxia - mitochondria - capillary - exercise - protein metabolism
