Are There Individual Differences In The Acute Muscle Swelling Response To Exercise With Blood Flow Restriction?

Low load exercise with blood flow restriction (BFR) acutely increases muscle swelling and chronically increases muscle size. The acute swelling is a possible mechanism for that muscle hypertrophy. It is thought that some individuals may respond differently when training with BFR. However, it is unknown if individual responses can be detected in a variable like acute swelling which has been linked with long term growth and whether relative pressures make this response more consistent. PURPOSE: To determine if differential responders can be detected in acute muscle swelling following LL-BFR and if relative pressures result in a more homogeneous effect. METHODS: 22 participants completed 5 visits. The first consisted of a limb arterial occlusion pressure (AOP) measurement, a unilateral one repetition maximum (1RM) test on a knee extension machine, and an endurance test consisting of 2 sets to failure with a low load (30%1RM) at 80% AOP. Each participant was randomly assigned to either complete visits 2-5 with a relative (80% AOP) or an absolute (100 mmHg) pressure. Each individual completed two control visits and two exercise visits. Muscle thickness was taken before and immediately after each condition. A one sample t-test determined whether there was an effect of treatment. A within-participant linear mixed model and a random-effects meta-analysis were used to quantify if the change was dependent on pressure applied and if change differed across individuals. RESULTS: Exercise resulted in an acute change in muscle swelling [0.33 (95%CI: 0.28, 0.38) cm]. This change did not depend upon the pressure application (100 mmHg: 0.35 cm vs. 80% AOP: 0.30 cm, p = 0.24). The linear mixed model did not support an individual response (participant * condition, p = 0.18), however, the random effects meta-analysis did when separated by the method of applied pressure. The τ2 value of 0.017 was statistically significant (p = 0.01) within the 100 mmHg condition but not with the 80% AOP (τ2 of 0, p = 0.81). CONCLUSION: There were similar mean changes in muscle swelling that did not depend on the method of pressure application. We noted greater variability within the absolute pressure group when compared to the relative pressure group. This may indicate a more homogeneous response between participants in this variable when relative pressures are used.