下坡跑誘發肌肉損傷對肌肉激素－irisin及肌肉合成指標之效應

Background: Irisin is a novel exercise-induced hormone secreted by skeletal muscle and possibly mediating the positive effects of exercise on metabolism via inducing “browning” of adipose tissue (Bostrom et al., 2012). Other than that, some studies had suggested that exercise-induced irisin may function as an exercise signal to facilitate muscle anabolism under muscle damage. Accordingly, possible influences of exercise-induced muscle damage and the repeated bout effect on irisin may need some investigating. Purpose: To examine the effects of single bout and repeated bouts of downhill running on blood irisin levels, muscle damage and other muscle growth-related factors. Methods: A total of 24 physically inactive young healthy men will be recruited and randomly separated into level running (LR, n=12) or downhill running groups (DHR, n=12). Each participant repeatedly completes two same bouts of exercise at 70% VO2max for 30 minutes, either at 0° (LR) or -15° (DHR) of slope on treadmill. Creatine kinase (CK), myoglobin (Mb), irisin, IGF-1, testosterone/cortisol ratio (T/C ratio) and growth hormone (GH) will be measured pre-exercise (Pre), immediately after (Post0), 1 hr after (1h), 24 hr after (24h) and 48 hr after (48h) each exercise bout. A three-way (group × time × bout) mixed ANOVA will be used for analyzing the collected data. Results: (1)DHR1: irisin at 24h, 48h were higher than Pre, Post0 (p < .05); DHR2: irisin at Post0, 1h were lower than Pre (p < .05)；(2) AUC-irisin over 48h was higher in DHR1 than in DHR2 (p < .05)；(3) irisin was positively correlated with testosterone (p < .05) and T/C ratio (p = .053) at 48h；(4) CK, Mb, soreness, IGF-1, GH, cortisol were higher in DHR1 than in DHR2 (p < .05)；(5) energy expenditure during exercise were not different among DHR1, DHR2, LR1 and LR2 (p > .05). Conclusion: The responses of irisin to downhill running were attenuated with repeated bout effect and might be correlated with muscle anabolism after exercise-induced muscle damage.