Assessment of fatigue-related biochemical alterations in a rat swimming model under hypoxia

It is well known that exercise-induced fatigue is exacerbated following hypoxia exposure and may arise from central and/or peripheral mechanisms. To assess the relative contribution of peripheral and central factors to exercise-induced fatigue under hypoxia, a rat model of fatigue by a bout of exhaustive swimming was established and fatigue-related biochemical changes in normoxic and severe hypoxic conditions were compared. Rats were randomly divided into four groups: normoxia resting (NR), exhaustive swimming (NE), hypoxia resting (HR) and exhaustive swimming (HE). The swimming time to exhaustion with a weight equal to 2.5% of their body weight reduced under hypoxia. There were lower blood lactate levels, lower gastrocnemius pAMPK/AMPK ratios and higher gastrocnemius glycogen contents in the HE than in the NE groups, which all suggested a lower degree of peripheral fatigue in the HE group than in the NE group. Meanwhile, there was a significant increase in striatal 3,4-dihydroxyphenylacetic acid (DOPAC) caused by exhaustive swimming under normoxia, whereas this increase was almost blunted under severe hypoxia, indicating that hypoxia might exacerbate exercise-induced central fatigue. These biochemical changes suggest that from normoxia to severe hypoxia, the relative contribution of peripheral and central factors to exercise-induced fatigue alters, and central fatigue may play a predominant role in the decline in exercise performance under hypoxia.