Intramuscular phosphate and pulmonary V̇O2 kinetics during exercise

Measurement of pulmonary oxygen uptake (V̇O₂) profiles during exercise provides a relatively simple, non-invasive and commonly employed strategy for assessing the integration of pulmonary, cardiovascular, neural and muscle-energetic systems in health and disease. However, the determinants of V̇O₂ response dynamics are less simple to localize and thus remain the source of much debate. Indeed these are not new issues; Krogh and Lindhard (1913), Hill and Lupton (1923) and later Hill (1926) recognized the importance of the dynamic phase of V̇O₂ and its role in determining the oxygen deficit at exercise onset (Krogh and Lindhard, 1913) and the oxygen debt (Hill, 1926) following cessation; that is the deficit being ‘re-paid’ as a debt at the cessation of exercise (Hill, 1926). Note that the term ‘O₂ debt’ suggested by Hill has been largely displaced by ‘excess post-exercise O₂ consumption’ (EPOC; Gaesser and Brooks, 1984). The term ‘EPOC’ has the advantage that its name does not suppose a mechanistic, and potentially erroneous, origin of the increased O₂ consumption post-exercise.