Purpose: There is conflicting evidence related to the prevalence and magnitude of exercise-induced muscle damage (EIMD) following four sets to volitional failure with BFR (BFR-F) or 75 total repetitions with BFR (1 × 30, 3 × 15, BFR-75). The purpose of this investigation was to examine muscle swelling, peak torque, and neuromuscular responses following BFR-75 and BFR-F.

Methods: Thirteen untrained women completed unilateral isokinetic (120°s−1) leg extensions concentric-eccentric at 30% of their maximal voluntary isometric contraction (MVIC) using BFR-75 and BFR-F protocols, separated by 15 minutes. Ultrasound was used to assess muscle thickness, cross sectional area, and echo intensity of the rectus femoris and vastus lateralis before, 0-, 24-, 48-, 72-, and 96-hours post-exercise. Peak torque and surface electromyography (sEMG) were recorded during MVICs before, 24-, 48-, 72-, and 96-hours post-exercise to determine sEMG amplitude, frequency, and neuromuscular efficiency.

Results: There were no differences between conditions. Collapsed across conditions, muscle thickness and cross-sectional area increased at 0-hours for the rectus femoris (2.5 ± 0.4, 2.8 ± 0.4 cm, 10.6 ± 1.8, 12.1 ± 1.8 cm2, respectively) and vastus lateralis (2.1 ± 0.5, 2.5 ± 0.7 cm; 22.2 ± 3.9, 25.1 ± 4.5 cm2, respectively), but returned to baseline at 24-hours. There were no changes in echo intensity, sEMG amplitude, sEMG frequency, or neuromuscular efficiency. MVIC peak torque increased relative to pre-exercise at 24-, 48-, 72-, and 96-hours (159.9 ± 34.9, 171.4 ± 30.1–179.1 ± 35.6 Nm).

Conclusion: These results suggest that BFR-75 and BFR-F did not cause EIMD but caused an acute increase in muscle swelling that returned to baseline 24-hours post-exercise.