Abstract
Residence at extreme altitude results in pronounced reductions in muscle mass and
the cross-sectional area of the slow and fast twitch fibre types. The reductions in
muscle contractile proteins appear not to be accompanied by significant alterations
in the proportion of the major fibre types and consequently in the myosin heavy chain
isozymes. Acclimatization to extreme altitude is also accompanied by a marked reduction
in mitochondrial potential that occurs regardless of activity status. At least during
mountaineering expeditions, the maximal activity of cytosolic enzymes involved in
anaerobic function appear to be unaffected. In contrast, extreme hypobaric hypoxia
with low exercise appears to result in loss of the activities of cytosolic enzymes.
The attentuation of glycolysis during exercise accompanying acclimatization does not
appear to be due to adaptations in fibre size, capillarization or mitochondrial potential.
Rather, evidence from both acclimatization and training at sea level suggests that
a depressed blood epinephrine concentration is involved.
Key words
Altitude - muscle - fibre type - metabolic pathways - lactate
