Endocrine responses to low-load blood flow restricted and high-load resistance exercise in well-trained males

The present study compared acute testosterone (T), cortisol (C), epinephrine (EPI), norepinephrine (NE), and 22 kDa growth hormone (GH-22 kDa) responses following low-load resistance exercise with blood flow restriction (LL-BFR) and traditional high-load resistance exercise (HL-RE). Twelve resistance-trained men performed bouts of LL-BFR (30%1RM) and HL-RE (70%1RM), each consisting of four sets of bilateral seated leg extensions taken to momentary task failure with 60 s rest periods. A randomized crossover design was used with time of day matched within-subjects. Upon arrival between 1200 and 1800, 24 h dietary recalls were performed with post-exercise blood samples obtained within 60 s (IP) and 5 min post-exercise (+5 min) via intravenous cannulation. Greater total repetitions (d = 2.37, p < 0.001) and less volume-load (d = 2.86, p < 0.001) were performed during LL-BFR. No Condition × Time interaction effects were found for any hormonal analyte measured (p > 0.05). Both LL-BFR and HL-RE elevate the potent β₂ adrenergic receptor (β₂AR) agonist EPI (IP: 1.29 ± 0.44 and 1.35 ± 0.60 nmol·L^-1, respectively), and the androgenic steroid T (+5 min: 27.4 ± 12.9 and 29.0 ± 14.3 nmol·L^-1, respectively). Thus, acute skeletal muscle β₂AR phosphorylation may be comparable between conditions. When lower resistance exercise intensities (e.g., 30% 1RM) are desired, athletes may perform LL-BFR in place of HL-RE and experience no statistical difference in acute endocrine responses.