Intermittent hypobaric hypoxia combined with aerobic exercise improves muscle morphofunctional recovery after eccentric exercise to exhaustion in trained rats

Unaccustomed eccentric exercise leads to muscle morphological and functional alterations, including microvasculature damage, the repair of which is modulated by hypoxia. Here we present the effects of intermittent hypobaric hypoxia and exercise on recovery from eccentric-induced muscle damage (EEIMD). Soleus muscles from trained rats were excised pre- (CTRL) and 1, 3, 7 and 14 days after a double session of EEIMD protocol. A recovery treatment consisting of one of the following protocols was applied one day after the EEIMD: passive normobaric recovery (PNR), a 4-hour daily exposure to passive hypobaric hypoxia at 4000m (PHR) or hypobaric hypoxia exposure followed by aerobic exercise (AHR). EEIMD produced an increase in the percentage of abnormal fibers compared with the CTRL; and affected the microvasculature by decreasing capillary density (CD, capillaries per mm²) and the capillary-to-fiber ratio (CF). After 14 days, AHR exhibited a CD and CF similar to the CTRL (789 and 3.30 vs. 746 and 3.06) and significantly higher than PNR (575 and 2.62) and PHR (630 and 2.92). Furthermore, VEGF expression showed a significant 43% increase in AHR when compared with PNR. Moreover, after 14 days, the muscle fibers in AHR had a more oxidative phenotype than the other groups, with significantly smaller cross-sectional areas (AHR: 3745; PNR: 4502; PHR: 4790 µm²), higher citrate synthase activity (AHR: 14.8; PNR: 13.1; PHR: 12 µmol·min^-1·mg^-1) and a significant 27% increment in PGC-1α levels compared with PNR. Our data show that hypoxia combined with exercise attenuates or reverses the morphofunctional alterations induced by EEIMD.

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