A Systematic Review with Meta-analysis of the Association between Changes in Muscle Strength and Clinical Outcome Changes in Patellofemoral Pain

OBJECTIVE: To investigate whether muscle strength changes observed in randomised controlled trials involving people with patellofemoral pain (PFP) are associated with concurrent changes in pain and physical function. DESIGN: Systematic review with meta-analysis, applying a two-stage structural equation modelling approach with random-effects estimation. ELIGIBILITY CRITERIA: Randomised clinical trials assessing non-surgical and non-pharmacological interventions that reported both muscle strength and at least one clinical outcome (pain or function) in people with PFP. DATA SOURCES: CINAHL, Cochrane Library, Embase, Medline and SPORTDiscus were searched from inception to April 2026. RESULTS: From 16,750 records screened, 82 trials met the eligibility criteria (4023 participants). Regarding self-reported pain outcomes, low to moderate evidence certainty indicated significant associations between strength improvements and pain reduction for knee extensors (r = - 0.75, β = - 0.21), knee flexors (r = - 0.46, β = - 0.14), hip abductors (r = - 0.91, β = - 0.31), hip adductors (r = - 0.26, β = - 0.19), hip external rotators (r = - 0.24, β = - 0.06), hip internal rotators (r = - 0.79, β = - 0.31) and hip extensors (r = - 0.58, β = - 0.26). Regarding self-reported function, low to high evidence certainty indicated that strength improvements in knee extensors (r = 0.70, β = 0.15), knee flexors (r = 0.46, β = 0.07), hip abductors (r = 0.94, β = 0.15), hip adductors (r = 0.55, β = 0.11), and hip internal rotators (r = 0.98, β = 0.06) were significantly associated with improved function. CONCLUSIONS: This review provides evidence that improvements in lower limb muscle strength are associated with improvements in pain and physical function among people with PFP. These findings reinforce the clinical relevance of strength-focused rehabilitation, particularly targeting the knee and hip muscles. REGISTRATION NUMBER: CRD42023420875.