Unilateral low-load blood flow restriction vs. high-load training in the Bulgarian split squat: a randomized within-subject design on strength, hypertrophy, and asymmetry

Purpose To compare the effects of a 6-week unilateral low-load blood flow restriction (LL-BFR) training protocol versus traditional high-load resistance training (HL-RT) on maximal strength, muscle hypertrophy, and explosive power in resistance-trained men. Methods Twenty-four resistance-trained males (age: 21.0 ± 2.0 years) completed a randomized within-subject trial. Each participant performed unilateral Bulgarian split squats (BSS) with one leg assigned to LL-BFR (30% 1RM, 30-15-15–15 repetitions at 80% arterial occlusion pressure [AOP]) and the contralateral leg to HL-RT (80% 1RM, 4 sets of 10 repetitions). Training consisted of 18 sessions over 6 weeks. Variable assessments, including BSS 1RM, vastus lateralis (VL) muscle thickness, and single-leg countermovement jump (SLCMJ) height and relative peak power were conducted both before (pretests) and after (posttests) the intervention. Results Both conditions resulted in significant time-dependent improvements in BSS 1RM (LL-BFR: +10.7%; HL-RT: +13.0%), VL muscle thickness (LL-BFR: +8.1%; HL-RT: +9.3%), and SLCMJ performance (height: +10.7–13.0%; relative peak power: +6.5–8.7%) (all P < 0.05). Crucially, no significant condition × time interactions were detected for any variable, indicating that the magnitude of adaptation was comparable between the LL-BFR and HL protocols. Additionally, training did not exacerbate inter-limb asymmetry. Conclusions Unilateral LL-BFR and HL-RT produced similar time-dependent improvements in maximal strength, muscle hypertrophy, and explosive performance in resistance-trained men. LL-BFR may be considered as a joint-sparing option when high mechanical loading is not feasible or desirable.