Intermittent hypoxic training: implications for lipid peroxidation inducedby acute normoxic exercise in active men

Oxidant generation during regular physical exercise training may influence the adaptive responses that have been shown to confer protection against ox idative stress induced by subsequent acute exercise. To examine this, we ra ndomly assigned 32 males to either a normoxic (n = 14) or a hypoxic (n = 18 ) group. During the acute phase, subjects in the hypoxic group performed tw o maximal cycling tests in a randomized double-blind fashion :one under con ditions of normoxia and the other under hypoxic conditions (inspired fracti on of O-2 = 0.21 and 0.16 respectively). During the intermittent phase, the normoxic and hypoxic groups each trained for 4 weeks at the same relative exercise intensity, under conditions of normoxia and hypoxia respectively. During acute exercise under hypoxic conditions, the venous concentrations o f lipid hydroperoxides and malondialdehyde were increased, despite a compar atively lower maximal oxygen uptake ((V) over dot O-2max) (P < 0.05 compare d with normoxia). The increases in lipid hydroperoxides and malondialdehyde were correlated with the exercise-induced decrease in arterial haemoglobin oxygen saturation (r = -0.61 and r = -0.50 respectively; P < 0.05), but no t with (V) over dot O-2max. Intermittent hypoxic training attenuated the in creases in lipid hydroperoxides and malondialdehyde induced by acute normox ic exercise more effectively than did normoxic training, due to a selective mobilization of x-tocopherol (P < 0.05). The latter was related to enhance d exercise-induced mobilization/oxidation of blood lipids due to a selectiv e increase in (V) over dot O-2max (P < 0.05 compared with normoxic group). We conclude that lipid peroxidation induced by acute exercise (1) increases during hypoxia; (2) is not regulated exclusively by a mass action effect o f (V) over dot O-2; and (3) is selectively attenuated by regular hypoxic tr aining. Oxidative stress may thus be considered as a biological prerequisit e for adaptation to physical stress in humans.