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.