Passive Blood Flow Restriction as a Countermeasure Against Disuse-Induced Muscle Atrophy: Physiological Mechanisms and Translational Evidence.

Abstract

Passive blood flow restriction (BFR)-intermittent vascular occlusion applied without voluntary contraction-has been proposed as a countermeasure against disuse-induced muscle atrophy in patients unable to perform conventional exercise. However, a comprehensive mechanistic synthesis integrating translational evidence with clinical applicability is lacking. This narrative review evaluated the physiological rationale, translational evidence, and safety considerations for passive BFR in load-restricted populations. PubMed/MEDLINE, Embase, and Web of Science were searched through April 2026. Studies investigating passive BFR in disuse or immobilisation contexts, together with mechanistic literature on relevant signaling pathways, were included. A three-tier evidence classification (direct, indirect, speculative) was applied throughout. Narrative synthesis followed Synthesis Without Meta-analysis (SWiM) reporting guideline due to substantial heterogeneity across study designs, populations, and protocols. Four mechanistic pathways were identified: metabolic stress and anabolic priming (indirect evidence), ischemia-reperfusion redox signaling (indirect evidence), neural modulation via metabolite-sensitive afferents (speculative evidence), and autocrine/paracrine responses (speculative evidence). The translational evidence revealed a consistent pattern: passive BFR attenuated muscle loss in postoperative (post-ACL, post-TKA) and critically ill populations characterized by elevated catabolic stress, but failed to preserve muscle mass during bed rest in healthy volunteers. To account for this divergence, a hypothesis-generating framework, the Catabolic Threshold Model is proposed, positing that passive BFR efficacy is gated by concurrent catabolic burden. A risk stratification framework including absolute and relative contraindications specific to passive BFR is presented; no serious adverse events were reported across published trials (cumulative n < 150), though safety reporting remains inconsistent. No formal risk-of-bias assessment was conducted, and the absence of reported events in such small samples should be interpreted as "no signal detected" rather than as evidence of safety. Passive BFR is a mechanistically plausible and apparently safe bridge intervention for the narrow therapeutic window between injury and active rehabilitation. Its clinical value appears contingent upon the presence of concurrent catabolic stress rather than mechanical unloading alone. Future mechanism-informed trials employing biomarker-guided patient stratification are needed to validate the Catabolic Threshold Model and establish standardised dosing protocols.