Effects of a low-load multi-component training program with blood flow restriction versus the same program without blood flow restriction on muscle thickness and functional outcomes in physically inactive young adults: randomized controlled trial

Introduction Low-load resistance training [≤50% one-repetition maximum (1-RM)] produces modest hypertrophic adaptations in untrained individuals. Blood flow restriction (BFR) training, combining low mechanical loads (30–40% 1-RM) with proximal limb occlusion, may augment these adaptations by inducing metabolic stress comparable to higher-load exercise. However, evidence comparing low-load multi-component training with and without BFR in physically inactive young adults remains limited. This study examined whether adding BFR to a standardized low-load training program enhances muscle thickness and functional performance outcomes compared with the same program performed without BFR. Methods In this single-blind randomized controlled trial conducted at Chongqing Medical University from November 2024 to November 2025, we enrolled 48 physically inactive physically inactive university-aged adults (25 males; mean age 18.98 ± 0.64 years). Participants were randomly assigned (1:1) to receive either low-load multi-component with BFR (n=24) or low-load multi-component without BFR) (n=24) training for 6 weeks (4 sessions/week). The BFR group trained at 30% (weeks 1-3) to 40% (weeks 4-6) 1-RM, with pneumatic cuffs inflated to 50% of individual arterial occlusion pressure. Outcomes were muscle thickness (ultrasound), and physical fitness tests. Results All 48 participants (mean age 19.0 ± 0.6 years) completed the 6-week intervention with ≥85% session attendance. The BFR group demonstrated significantly greater muscle thickness increases compared with without-BFR group in bilateral biceps brachii (right: +0.45 cm vs +0.11 cm, P = 0.001, ηp 2 =0.20; left: +0.37 cm vs +0.10 cm, P = 0.001, ηp 2 =0.21) and right rectus femoris (+0.13 cm vs +0.02 cm, P = 0.001, ηp 2 =0.17). Functional performance improvements favoring BFR included left-hand grip strength (+3.63 kg vs +1.09 kg, P = 0.001, ηp 2 =0.28), bilateral thigh circumference (P = 0.001, ηp 2 =0.12), and exercise-specific core training (males: pull-ups +5.92 vs +2.08 repetitions; females: abdominal curls +11.18 vs +3.33 repetitions). Between-group differences reached significance for 10 of 18 primary and secondary outcomes (56%). Seven BFR participants (29%) reported minor, transient discomfort during week 1; no serious adverse events occurred. Conclusion Adding BFR to low-load multi-component training produced greater improvements in limb muscle thickness and functional performance compared with the same training performed without BFR in physically inactive young adults over 6 weeks. Benefits were most evident in upper extremity hypertrophy and task-specific functional capacity, with 56% of outcomes demonstrating significant between-group differences favoring BFR. The intervention was well-tolerated with no serious adverse events. These findings support BFR-enhanced low-load training as a potential alternative for individuals unable or unwilling to engage in high-load resistance training, though generalizability to other populations and longer-term sustainability require further investigation. Clinical Trial Registration https://www.thaiclinicaltrials.org/ , identifier TCTR20241110003.