Exercise-Induced Hypoalgesia Following Blood Flow Restricted Exercise Among People Living With Multiple Sclerosis

PURPOSE: Pain is a frequent symptom of multiple sclerosis (MS). Various treatments, including exercise (exercise-induced hypoalgesia [EIH]), can be used to manage pain. One method of achieving EIH is using blood flow restriction (BFR) during exercise, but evidence of its effectiveness for patients with MS is limited. Therefore, the purpose of this investigation was to evaluate EIH after BFR, low load (LL), and high load (HL) resistance exercise in individuals with MS. METHODS: 13 females and 3 males (41 ± 10 years; 172.0 ± 11.6 cm; 87.0 ± 18.9 kg) with relapsing-remitting MS completed three separate exercise visits involving isotonic unilateral leg extensions. Participants completed BFR (1 × 30, 3 × 15, 30% of 1 repetition maximum [1RM]), LL (1 × 30, 3 × 15, 30% of 1RM), and HL (3 × 12, 70% of 1RM) in a randomized order. Pain pressure threshold (PPTr) and tolerance (PPTo) of the rectus femoris were assessed before and after each exercise visit to quantify the EIH response. After each set of exercise, participants rated their pain on a visual analog scale (0-10). Separate one-way ANOVAs were used to compare changes from pre-exercise PPTr and PPTo values and mean pain during exercise. Mediation analyses were used to evaluate the relationship between exercise intervention and changes in PPTr and PPTo with mean pain as a mediator. RESULTS: There was a significant (p = 0.039) difference in mean pain between exercise interventions. Mean pain was significantly (p = 0.032) higher during BFR (3.2 ± 2.4 au) than HL (1.3 ± 1.5 au). For PPTr and PPTo, there was a significant (p = 0.030 - 0.040) difference between exercise interventions. PPTr and PPTo change were significantly (p = 0.027 - 0.031) greater following BFR (1.3 ± 0.9 Δkgf; 1.9 ± 1.2 Δkgf, respectively) than LL (0.3 ± 0.7 Δkgf; 0.2 ± 1.8 Δkgf. respectively). For the mediation analyses, the confidence intervals for the estimate of the coefficient of the indirect effect of mean pain on PPTr and PPTo contained zero, indicating mean pain during exercise did not significantly mediate the relationship between exercise interventions (BFR and HL) and PPTr or PPTo. CONCLUSION: BFR is an effective training modality for achieving EIH in individuals with MS while using lower loads (30% of 1RM). Furthermore, pain during exercise was not a significant mediator of EIH suggesting other mechanisms may be involved.