Skeletal muscle adaptations following blood flow-restricted training during 30 days of muscular unloading

This study evaluated the effectiveness of low-load resistance training with a blood flow restriction (LL_BFR) to attenuate muscle loss and weakness after 30 days of unilateral lower limb suspension (ULLS). Sixteen subjects (ages 18-50 yr) underwent 30 days of ULLS. Measurements of muscle strength, cross-sectional area, and endurance on the knee extensors and plantar flexors were collected before and after ULLS. Plasma concentrations of IGF-1 and IGFBP-3 were also assessed. During ULLS, eight subjects (5 males, 3 females) participated in LLBFR three times per week (ULLS + Exercise) while eight subjects (4 males, 4 females) did not exercise (ULLS). The blood flow-restricted exercise consisted of dynamic knee extension at 20% of the subject's isometric maximum voluntary contraction coupled with a suprasystolic blood flow restriction. After 30 days of limb suspension, the ULLS + Exercise group experienced minimal and insignificant losses in knee extensor cross-sectional area and strength (1.2% and 2.0%, respectively; P ≤ 0.05), while the ULLS group demonstrated significant reductions in cross-sectional area and strength (7.4% and 21%, respectively). Decrements in plantar flexor strength (23.7%) and cross-sectional area (7.4%) were observed after ULLS (P < 0.05) and were of similar magnitude between the experimental groups (P > 0.05). Muscular endurance in the knee extensors improved 31% in the ULLS + Exercise group, while it decreased 24% in the ULLS group (P = 0.01). No changes were seen in hormone concentrations throughout the study. In conclusion, LL_BFR of the knee extensors is effective in maintaining muscle strength and size during 30 days of ULLS and results in improved knee extensor muscular endurance.