Abstract
Background
Exercise-induced hypoalgesia (EIH) is vital for rehabilitation, but its efficacy in patients with knee pain remains controversial. Blood flow restriction (BFR) might augment analgesia through metabolic accumulation. This study aimed to investigate the acute analgesic impact of a low-intensity warm-up with or without BFR and to compare EIH responses between healthy individuals and patients with persistent knee pain.Methods
Forty-six participants (healthy controls: n = 26; participants with persistent knee pain: n = 20) were enrolled in a single-session, within-subject split-body protocol. BFR at 70% arterial occlusion pressure was applied to one limb during a 5-min low-intensity warm-up. The BFR-treated limb was randomized in healthy controls, whereas in participants with persistent knee pain, BFR was consistently applied to the symptomatic limb, with the contralateral asymptomatic limb serving as the within-subject comparison. Pressure pain thresholds (PPT) were measured at three peri-patellar sites pre- and post-condition using a Latin Square design. Data were analyzed via Linear Mixed Models.Results
Healthy controls showed a robust increase in PPT after warm-up (+ 5.55 N, 95% CI, 4.20 to 6.90), whereas participants with persistent knee pain showed no clear increase (+ 0.15 N, 95% CI, -1.39 to 1.69). The between-group difference in EIH was significant (+ 5.40 N, 95% CI, 3.36 to 7.45, p Conclusion
A brief low-intensity warm-up induced a clear EIH response in healthy controls, whereas participants with persistent knee pain showed a markedly attenuated response. The tested BFR protocol did not demonstrate statistically superior additional hypoalgesic effects compared with the non-BFR condition. These exploratory findings warrant further investigation using adequately powered, prespecified, and mechanistically informed studies.Trial registration
Chinese Clinical Trial Registry ChiCTR2300069386 ( https://www.chictr.org.cn/ , registered on 15 March 2023).