Objective: The purpose of this systematic review with meta-analysis was to compare the effects of low load resistance combined with blood flow restriction (BFR) versus conventional quadriceps strengthening on knee symptoms and function as well as knee extensor strength and muscle thickness in adults with knee conditions.
Literature survey: Guidelines based on the latest evidence highlight the importance of quadriceps strengthening to reduce pain and improve function in patients with knee conditions. Blood flow restriction is based on brief periods of vascular occlusion which cause muscle hypertrophy and increased strength. Before it can be recommended for individuals with knee conditions, quadriceps strengthening with low load resistance combined with BFR (LL-BFR) must show beneficial effects on clinical outcomes in addition to quadriceps strength and mass.
Methods: A systematic review with meta-analysis was conducted to identify relevant studies through PubMed, PEDro, and ScienceDirect up to January 2019. The protocol was registered on PROSPERO (CRD42019121306). Differences in pre- and post-intervention means and standard deviations were extracted to calculate the standardized mean difference for each intervention in each included study.
Synthesis: Eight studies were included. Limited evidence suggests that LL-BFR is more beneficial on quadriceps strength and thickness in patients with knee conditions than LL training alone or in addition to a rehabilitation program. Limited evidence indicates that LL-BFR training is equally effective in improving function and muscle thickness compared with a HL quadriceps strengthening program but elicits less knee pain, corresponding to additional benefits of 22 (95% confidence interval 1 to 43) mm on a 0-100 mm visual analogue scale.
Conclusions: BFR could be a useful option for patients with knee conditions where conventional quadriceps strengthening program exacerbate knee symptoms. Future investigations should compare different BFR protocols to help establish better guidelines for clinicians.
Keywords: Knee; quadriceps; rehabilitation; strengthening.