Impact of blood flow restriction training timing: Does exercising at dusk or dawn enhance response?

Data suggest that skeletal muscles have an internal clock that dictates training-related adaptations, which could generate different health benefits in response to exercise timing. However, limited data exist on the impact of blood flow restriction (BFR) training timing on health outcomes. To investigate the impact of 6 weeks of BFR training performed at different times of day on body composition, performance measures, and irisin and PGC1-α4 expression. Participants (n = 31; aged 19-30) who performed 6 weeks of BFR resistance training were categorized into morning (n = 16; 05:00-11:00) or afternoon (n = 15; 11:00-17:00) groups. A sub-analysis of responders and non-responders (top and bottom 25% of muscle strength or lean mass change) was performed. Primary outcomes were changes in body composition, muscle strength, isokinetic measures, and irisin and PGC1-α4 expression. Time effects were observed for changes in lean mass (p < 0.001), relative lean mass (p < 0.001), body fat percentage (p = 0.02), and all performance measures (ps ≤ 0.015). A negative correlation was observed between lean mass change and irisin change (r = -0.18; p = 0.57). No group or time × group interactions were reported for any outcomes. Six weeks of BFR training provided improvements in body composition and performance outcomes and no changes in irisin and PGC1-α4 irrespective of timing.