Impact Of Blood Flow Restriction Training Performed At Different Times Of Day On Performance

Recent data suggest skeletal muscles have an internal clock that dictates health-related adaptations. Therefore, exercise training at different times of the day may generate different health benefits and myokine release. However, little data exists on how the time of day of exercise may impact males and females, specifically using blood flow restriction (BFR) training. PURPOSE: To investigate the impact of a 6-week BFR exercise intervention performed at different times of day on body composition, isokinetic measures, and irisin expression in young, healthy adults. METHODS: A single-arm intervention of 6-week BFR resistance training was performed three times per week. Participants (n = 31; aged 19-30) were categorized into morning (05:00-11:00, n = 16) or afternoon (11:00-17:00, n = 15) group. A sub-analysis of responders and non-responders (top and bottom 25% of muscle strength) was performed on a random sample of individuals from the morning and afternoon groups. Primary outcomes were changes in body composition (dual-energy X-ray Absorptiometry), total work, average power, peak torque (Humac Norm Isokinetic Dynamometer) and irisin expression (western blot). RESULTS: No significant differences between groups were observed at baseline. A significant improvement was observed for both groups for change in lean mass (AM: p = 0.006, PM: p = 0.011) and lean mass/height2 (AM: p = 0.005, PM: p = 0.013). A significant improvement was observed for the morning group for trunk lean mass (p = 0.012), total work of flexors (p = 0.02) and extensors (p = 0.012), average power of flexors (p = 0.003) and extensors (p = 0.004), and peak torque of flexors (p = 0.004) and extensors (p = 0.038). A significant decrease was observed in the afternoon group for body fat percentage (p = 0.049). Responders’ who performed BFR in the morning had approximately a 1.2-fold (p = 0.012) increase in irisin compared to non-responders. CONCLUSION: This study demonstrates that there is no difference in performance outcomes when young, healthy individuals exercise with BFR at different times of day. People who respond to BFR in the morning have a greater irisin expression. Healthy Seniors Pilot Project, CIHR, Public Health Agency of Canada