Beetroot juice supplementation enhances the effects of blood flow restriction training on lower limb strength and vertical jump performance under fatigue in male university students: a randomized, double-blind, placebo-controlled study.

内容摘要

Beetroot juice (BRJ) supplementation has the potential to enhance the effects of blood flow restriction (BFR) training in improving muscle strength and fatigue resistance; however, evidence supporting their combined effects remains limited. This study investigated whether BRJ supplementation enhances the effects of BFR training on muscle strength and fatigue resistance. This randomized, double-blind, placebo-controlled trial included 20 male university students from the School of Sports, who were randomly assigned to a BFR group (n = 10, age: 21.9 ± 1.7 years) or a BFR + BRJ group (n = 10, age: 21.8 ± 1.5 years; nitrate: 8 mmol/day). Participants completed a one-week BRJ pre-supplementation phase followed by a four-week bilateral knee extensor/flexor BFR training program (40% limb occlusion pressure, 30% of peak torque load), performed three times per week. Knee extensor and flexor strength (at 60°/s, 180°/s, and MVIC) and countermovement jump (CMJ) performance were assessed using an isokinetic dynamometer and a force plate pre- and post-intervention. Both the four-week BFR and BFR+BRJ interventions significantly increased the relative peak torque of the knee extensors/flexors at 60°/s (Left: ppre-post = 0.23, d = -0.89, ηp²Time = 0.775; Right: ppre-post = 0.017, d = -0.63, ηp²Time = 0.744), 180°/s (Left: ppre-post = 0.028, d = -1.32, ηp²Time = 0.319; Right: ppre-post = 0.007, d = -1.48, ηp²Time = 0.822), and MVIC (Left: ppre-post = 0.007, d = -0.11, ηp²Time = 0.825; Right: ppre-post = 0.009, d = -1.31, ηp²Time = 0.842). They also improved the torque of the knee extensors in both the left and right legs during the 100-repetition maximal voluntary contraction test at 90°/s, with both initial (first 20 reps) and final (last 20 reps) values significantly increased (Left: ppre-post = 0.029, d = -0.96, ηp²Time = 0.612; Right: ppre-post = 0.007, d = -1.21, ηp²Time = 0.725). The CMJ test showed significant improvements in fatigued bilateral CMJ height (ppre-post = 0.048, d = -0.534, ηp²Time = 0.556), peak force (ppre-post = 0.047, d = -0.913, ηp²Time = 0.444), and rate of force development (RFD; ppre-post = 0.044, d = -0.902, ηp²Time = 0.656) following both BFR and BFR + BRJ interventions. Notably, single-leg countermovement jump performance showed no significant improvements for either the left or right leg. Notably, post-intervention, only the BFR+BRJ group showed significant improvements in fatigued bilateral CMJ height (ppre-post = 0.012, d = -1.307, ηp²Time = 0.846). The results indicate that four weeks of BFR training, with or without BRJ supplementation, can improve knee flexor and extensor strength and bilateral CMJ performance. However, the effects of BRJ were selective rather than broadly superior, as BRJ mainly enhanced BFR training by reducing fatigue-related declines in vertical jump performance.