Autophagy is Stimulated by Acute High-Intensity Interval Training Exercise in Human Skeletal Muscle
Exercise Science and Sport Management
Autophagy is an evolutionary conserved cellular degradation system implicated in maintaining health and promoting longevity. Few human data exist investigating the autophagic response to exercise; however, acute moderate-intensity, continuous exercise (MICT) has been shown to stimulate autophagy in skeletal muscle. Presently, it is unknown whether high-intensity interval training (HIIT) exercise induces autophagy. PURPOSE: The purpose of this study was to compare the autophagy response of an acute bout of HIIT exercise (treadmill running) to MICT exercise in human skeletal muscle. METHODS: Using a crossover design, ten recreationally-active males (n=5) and females (n=5) performed a bout of MICT (60 minutes at 55% of max velocity [Vmax]]) and HIIT (6 bouts of 1 minute at 100% Vmax and 1 minute at 3 MPH, followed by 5 minutes at 3 MPH, followed by 6 bouts of 1 minute and 100% Vmax and 1 minute at 3 MPH). Muscle biopsies from the vastus lateralis were taken pre- and 3 hours post-exercise. Exercise bouts were separated by ≥72 hours and performed after abstaining from alcohol for ≥24 hours and food and caffeine for ≥8 hours. Subjects also refrained from food, energy-containing beverages, and caffeine during the 3-hour post-exercise period prior to the muscle biopsy. Muscle tissue was analyzed for protein expression of markers of autophagy (LC3I, LC3II) and autophagy signaling (p38MAPK) via western blot analysis. RESULTS: No differences were detected for LC3I, LC3II, and p38MAPK protein content measured 3 hours post-exercise compared to pre-exercise in both HIIT and MICT bouts (p>0.05). LC3II:LC3I ratio increased 3 hours post-exercise in HIIT (162.4 ±: 45.9%), which was significantly higher than MICT at 3 hours post-exercise which decreased from pre-exercise (48.8± 9.4%; p<0.05). CONCLUSION: Our findings show that despite discrepant durations and intensities, HIIT stimulates autophagy in human skeletal muscle, however, in a distinct fashion compared to MICT. Our data also add to the current literature demonstrating that autophagy is activated by continuous (≥ 60 minutes), moderate-intensity (55 - 70% VO2max) exercise.
Medicine & Science in Sports & Exercise
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