Exercise Physiology: Exercise performance at altitude

This review explores recent advances in the etiology of exercise intolerance (classically defined by a reduced maximal or peak oxygen uptake) in lowlanders at high altitudes, focussing on sites of physiological-system limitation and how these may differ in highlanders. The traditional opinion of impaired oxygen delivery along a convective-diffusive cascade between lungs and exercising-muscle mitochondria remains relevant but an oversimplification. Thus, developments in genomics, proteomics and metabolomics are providing an exciting, expanded perspective of exercising-muscle function. However, factors such as ascent profile, altitude sojourn, training status, ethnicity, genetics and development present interpretational challenges. Also, while animal models can be useful proxies for human function because they allow a greater degree of invasive interrogation, species differences can limit their applicability. Finally, assessment of exercise performance at altitude requires rigorous application of exercise intensity, through key demarcators such as the lactate threshold, critical power and W' - each of which are altitude-dependent.