Exercise-induced Hypoxia and Structural and Metabolic Adaptation of Skeletal Muscle

We hypothesised that elevated oxygen concentration during exercise on rats exhibits smaller muscle structural and metabolic adaptations of skeletal muscles than rats under the same training protocol in normoxia. Changes in m. tibialis anterior after 6-week training by swimming under hyperoxic condition (SO) were compared with those trained in normoxia (SN) and sedentary control rats (C). Capillary-to-fibre ratio was increased in SO and SN group as compared to C. The cross-sectional area was significantly increased in fast glycolytic (FTb) fibres of SO and SN but not in FTa fibres. Myoglobin (MG) concentration in SN was 21% higher in the fast oxidative (FTa) fibres, as well the succinate dehydrogenase (SDH), cytochrome c oxidase (cyt.c) and α-glycerophosphate dehydrogenase (α-GPDH) activity were 18, 56 and 45% higher respectively, than in C group (p < 0.05). Cyt.C and α-GPDH activity in FTb fibres in SN were 69 and 40% higher respectively than in C animals (p < 0.05). No significant changes were found either in SDH or α-GPDH activities or MG content in SO animals compared to the C. In conclusion, hypoxia arising in muscles during training stimulates those changes that promote better substrate and oxygen supply to muscles and better oxygen transport within fibres. Apparently, initiation of capillary growth is determined by factors other than hypoxia.