Protein supplementation optimizes muscle strength and hypertrophic responses induced by low-load training with blood flow restriction in resistance-trained individuals.

Abstract

Background & aims: Low-load blood flow restriction (LL-BFR) training induces favorable changes in muscle hypertrophy and strength. However, the potential additive effect of LL-BFR and protein supplementation on these outcomes remains unclear.

Methods: Twenty-four recreationally resistance-trained men were randomly assigned to either a protein (PRO) or placebo (PLA) supplementation group in a 2:1 ratio. After being submitted to maximum dynamic strength (1-RM) and elbow flexors muscles cross-sectional area (EFCSA) assessments at baseline, participants were enrolled in a 3-week unilateral LL-BFR training (4 days per week, 4 sets of 15 repetitions, 30% 1-RM) for the elbow flexors muscles in the incline dumbbell curl exercise. Psychological outcomes (rate of perceived exertion, pain and muscle soreness) were obtained at the first and last training session. EFCSA and 1-RM were reassessed after LL-BFR, with EFCSA being assessed at 45%, 65% and 85% of humerus length.

Results: Psychological responses to LL-BFR improved in PRO and PLA (both p<0.05), with no significant between-group differences (all comparisons, p>0.05). A significant improvement in 1-RM was detected for PRO (+7.2%, p=0.0002), but not PLA (+3.5%, p=0.156). PRO experienced significant increases in EFCSA at 45% (+7.5%, p=0.021), 65% (+5.2%, p=0.033) and 85% lengths (+8.4%, p=0.002), while PLA experienced increases only at the 85% length (+5.9%, p=0.045). Absolute increases in 1-RM were greater for PRO vs. PLA (p=0.039), whereas increases in EFCSA tended to be greater for PRO vs. PLA at 45% (p=0.086) and 65% lengths (p=0.072).

Conclusion: Our results showed that protein supplementation optimized the LL-BFR-induced muscle strength and hypertrophy improvements in trained individuals under comparable psychological responses.