Strengthening exercises improve knee muscle strength and performance but not pain in ACL-reconstructed individuals: A systematic review and meta-analysis of randomised controlled trials

Abstract

Purpose: Deficits in quadriceps and hamstring strength, functional performance and pain are common after anterior cruciate ligament reconstruction (ACLR). The role of strengthening exercises (SE) in addressing these outcomes remains uncertain. This systematic review and meta-analysis aimed to evaluate the effects of SE on quadriceps and hamstring strength, functional performance and pain in individuals after primary ACLR. Methods: Four databases (PubMed, Web of Science, Scopus and Embase) were searched from inception to July 2025. Eligibility criteria included randomised controlled trials (RCTs) on adults with ACLR evaluating SE versus conventional rehabilitation. Data extraction followed PRISMA 2020 guidelines. The risk of bias was assessed using the Cochrane PEDro scale. Random-effects models were used to calculate standardised mean differences (SMD) with 95% confidence intervals (CI). Heterogeneity was assessed with I², and subgroup/sensitivity analyses and publication bias were performed. Results: Nineteen RCTs (n = 818) were included. SE significantly improved quadriceps strength (SMD: 0.76; 95% CI: 0.46 to 1.05; p < 0.01; I² = 0%, p = 0.48) and hamstring strength (SMD: 0.70; 95% CI: 0.41 to 1.0; p < 0.01; I² = 0%, p = 0.43). Functional performance (single-leg hop test, Lysholm score, ADL questionnaire, ROM extension) also improved with SE. However, knee pain outcomes showed no significant changes (SMD: −0.32; 95% CI: −0.98 to 0.34; p = 0.34; I² = 86%, p < 0.01). Conclusions: SE significantly enhances knee strength and functional performance in individuals with ACLR, although their effects on pain remain unclear. Clinically, incorporating SE into rehabilitation protocols is recommended to improve recovery outcomes, accelerate return to sport (RTS) and enhance readiness. Further studies are warranted to clarify their impact on pain management. Level of Evidence: Level I.