Abstract
[Purpose]To determine the effects of exercise-induced muscle damage, we examined irisin responses during level running (LR), with less muscle damage, and downhill running (DHR), with greater muscle damage under equivalent exercise duration and oxygen consumption (⩒O2) conditions.[Methods]Fifteen healthy men (age: 21.6 ± 2.0 y, height: 170 ± 1.3 cm, weight: 64.8 ± 2.7 kg) were randomly assigned to either the LR group (n = 8) or the DHR group (n = 7). Subjects in the LR group performed treadmill running at 70% of maximum oxygen uptake (⩒O2max) for 30 min on a 0% gradient. In contrast, subjects in the DHR group performed the same exercise on a –10% gradient. Blood samples were collected before exercise, immediately after exercise, and 1, 3, and 24 h after exercise.[Results]No significant interaction (group × time) or main effect of group or time was observed for changes in plasma irisin concentrations over time (P > 0.05). However, the area under the curve of plasma irisin concentrations during a 3-h post-exercise period was significantly greater in the DHR (239,197 ± 8,166 ng/mL) group than in the LR (92,293 ± 8,755 ng/ml) group (P < 0.05). The blood lactate, serum cortisol, myoglobin, and plasma interleukin-6 concentrations were significantly higher in the DHR group than in the LR group after exercise (P < 0.05 for all variables).[Conclusion]DHR associated with marked muscle damage promoted a greater increase in exercise-induced irisin did LR after the same duration under identical VO2 conditions.
Highlights
Myokines are physiologically active substances released from skeletal muscle[1]
The serum creatine kinase (CK) concentration did not exhibit a main effect for time (P = 0.12, η2 = 0.17). This is the first study to explore the effects of exercise-induced muscle damage on the irisin response
The exercise-induced irisin response over 3 h after downhill running (DHR) was significantly greater than that after level running (LR), suggesting that the augmented irisin response may be associated with magnitude of muscle damage
Summary
Myokines are physiologically active substances released from skeletal muscle[1]. Irisin is a relatively recently discovered myokine that enhances energy expenditure (EE) by increasing UCP1 expression in white and/or beige adipocytes[2,3]. Several studies have described the irisin response to a single bout of exercise[4,5,6,7,8,9,10]. A single bout of resistance exercise (6–8 exercises) significantly increased the irisin response[13,14]. Differences in the exercise-induced irisin response among various studies may be explained by the different exercise modalities, with varying degrees of eccentric contraction. Fast-twitch fibers are more prominently recruited than during concentric contraction[15,16,17,18]. An increase in exercise intensity promotes recruitment of fast-twitch fibers, leading to an augmented irisin response[19]
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