Blood Flow Restriction Training Induces Morphological And Strength ADAPTations In Military Personnel With Persistent Pain.

PURPOSE: Lower limb muscle strength is a key focus of rehabilitation from knee injuries, yet conventional heavy load resistance training (HL-RT) is often contraindicated due to pain. Low load blood flow restriction training (LL-BFR) is an alternative exercise modality that has induced positive musculoskeletal adaptations in the absence of heavy loads. However, the efficacy of intensive LL-BFR in the UK military rehabilitation care pathway remains unknown. This multi-centre (four study site) randomised control trial (RCT) was designed to test the hypothesis that LL-BFR will result in comparable morphological and strength adaptations versus HL-RT in patients undergoing a 3-week residential rehabilitation course. METHODS: Seventeen male UK military personnel (n = 8 LL-BFR, n = 9 HL-RT) with persistent knee pain received either a) twice-daily LL-BFR or b) a work-matched thrice-weekly HL-RT intervention. The primary outcome was quadriceps femoris (QF) muscle volume (via MRI imaging). Secondary outcomes included peak knee extensor torque during a maximum voluntary isometric contraction (MVIC) and net peak force during an isometric mid-thigh pull (IMTP). Outcomes were assessed pre- (T1) and post- (T2) the 3-week intervention. A 2 x 2 (group x time) mixed ANOVA assessed changes in outcome variables between T1 and T2, with magnitude of change reported as a percentage. RESULTS: There were no between group differences at baseline. QF volume increased from T1 to T2 in the LL-BFR (7.9 ± 2.6%, p < .001) and HL-RT group (4.6 ± 4.0%, p = .004), with no group x time interaction (p = .085). Knee extensor MVIC and IMTP net peak force increased from T1 to T2 in the LL-BFR group (31.2 ± 20.0%, p < .001, and 17.9 ± 8.2%, p < .001, respectively), but not in the HL-RT group (14.1 ± 20.5%, p = .085, and 5.9 ± 14.5%, p = .145, respectively), with a significant group x time interaction for MVIC (p = .026) and IMTP (p = .031). CONCLUSIONS: Our findings suggest that high frequency LL-BFR produces a comparable increase in QF muscle volume (hypertrophy), but greater improvements in measures of muscle strength versus HL-RT in individuals with persistent knee pain. Performing twice-daily LL-BFR over a short duration (3-weeks) may provide a suitable alternative training modality, particularly when heavy loads are unattainable due to pain or functional limitations.