The Acute Muscle Swelling Response: The Influence Of Sex And Cuff Size

Abstract

Muscle cell swelling is a purported mechanism for the muscle hypertrophy following blood flow restriction (BFR) training. There are numerous cuff widths used in literature in BFR. It is presently unknown if cuff width impacts the swelling response and whether this differs between sexes. PURPOSE: To examine whether the acute muscle swelling response differs based on cuff size and sex. METHODS: Forty-nine (25 men, 24 women) participants completed two conditions in a random order (one each arm). Participants completed four sets of unilateral elbow flexion exercise to failure using 30% of their one repetition maximum with BFR applied with either a narrow (5cm) or a wide (12 cm) cuff inflated to 40% of the arterial occlusion pressure. Muscle thickness and echo intensity were measured before and after each exercise bout in the supine position. A repeated measures analysis with a between subject factor of sex was used to assess changes between conditions. Default priors were used for fixed effects (r=0.5) and random effects (r=1). Bayes Factors (BF10) were used to quantify evidence for the null and alternative hypothesis. Data are presented as mean (SD) unless otherwise stated. RESULTS: For muscle swelling, there was evidence for an interaction. Men had greater swelling than women [Men: 0.57 (0.18) vs. Women: 0.39 (0.15) cm] with the narrow cuff [median δ (95% credible interval) .903 (.324, 1.52); BF10: 38.57]; but there was no evidence of a difference within the wide cuff [median δ (95% credible interval) .348 (-.170, .902); BF10: .690]. There was some evidence that men had greater swelling with the narrow [0.57 (0.18) cm] cuff compared to the wide [0.49 (0.14) cm] cuff [median δ (95% credible interval) .602 (.071, 1.174); BF10: 2.61]. However, there was no evidence (BF10: .439) for this in women [Narrow: 0.39 (.15) vs. Wide: 0.43 (.12) cm]. For changes in echo intensity, there was no evidence for an interaction or an effect of cuff [Narrow: 1.2 (8) vs. Wide: -.5 (7) AU, BF10: .41]. There was evidence for the null with sex (BF10: .322). CONCLUSIONS: Acute muscle swelling occurs in both men and women, even when using a wide cuff. There is evidence, however, that the change in swelling is greater in men, particularly with the narrow cuff. Whether these acute changes translate to differences in chronic adaptations is currently unknown.