Blood Flow-restricted Exercise Does Not Induce a Cross-Transfer of Effect: A Randomized Controlled Trial

Abstract

Purpose: The goal of this trial was to determine whether low-load blood flow-restricted (BFR) exercise of appendicular muscles induces a cross-transfer of effect to the trunk extensor (TE) muscles, such that low-load TE exercise would enhance TE size and function to a greater extent than standard low-load exercise in people with recurrent low back pain (LBP). We also investigated the direct effects of BFR exercise in the appendicular muscles.

Methods: Thirty-two adults with recurrent, nonspecific LBP were randomized into two groups: Appendicular BFR exercise (BFR exercise) or control exercise (CON exercise). All participants trained (two times per week) for 10 wk, with a 12-wk follow-up. Participants performed three sets of leg extension (LE), plantar flexion (PF), and elbow flexion (EF) exercises followed by low-load TE exercise without BFR. Outcome measures included magnetic resonance imaging-derived muscle size (quadriceps and TE), strength (LE, PF, EF, and TE), and endurance (LE and TE).

Results: There was no evidence for a cross-transfer of effect to the TE. There was also no statistically significant enhancement of limb skeletal muscle size or function of BFR relative to CON exercise at any time point; though, moderate effect sizes for BFR exercise were observed for enhanced muscle size and strength in the leg extensors.

Conclusions: Low-load BFR exercise of the appendicular muscles did not result in a cross-transfer of effect to the TE musculature. There was also no significant benefit of low-load BFR exercise on the appendicular muscle size and function, suggesting no benefit from low-load BFR exercise in adults with recurrent, nonspecific LBP.

FIGURE 1

BFR exercise did not result in a significant cross-transfer of effect in erector spinae muscle CSA. Error bars represents 95% CI. 95% CI, 95% confidence interval.

FIGURE 2

BFR exercise did not result in a significant cross-transfer of effect in TE muscle strength (A) or endurance (B) (note that beneficial effects noted in the follow-up period are in the CON exercise group). Error bars represents 95% CI.

FIGURE 3

BFR exercise did not significantly increase quadriceps femoris muscle CSA. Error bars represents 95% CI.

FIGURE 4

Effect of BFR exercise on appendicular muscle strength of the leg extensors (A), plantar flexors (B), and elbow flexors (C). Panel D illustrates the effect of BFR exercise on leg extensor (LE) muscle endurance. For plantar flexor strength and leg extensor endurance the control exercise group exhibited a significant increase postexercise (*plantar flexor, P = 0.05; leg extensor endurance, P = 0.04); however, the group difference was only significant for the plantar flexors (plantar flexor group difference, P = 0.05, η² = 0.84; leg extensor endurance group difference, P = 0.2; η² = 0.39). Error bars represents 95% CI.