Effectiveness of muscle strengthening exercises on the clinical outcomes of patients with knee osteoarthritis: A randomized four-arm controlled trial.

Background: Knee osteoarthritis (OA) is one of the major causes of dysfunction that reduces patients' quality of life. The aim of current study was to investigate the effectiveness of muscle strengthening exercises on the clinical outcomes of patients with knee OA. Methods: We conducted a single-blind clinical trial on 96 patients with mild to moderate knee osteoarthritis. Patients were randomly assigned to 4 groups with 24 patients and followed-up for 8 weeks. Quadriceps, hamstring and both hamstring and quadriceps strengthening exercises were received by the first (G1), second (G2) and third (G3) groups, respectively. The fourth group (G4) was the control group and did not receive any intervention. The main outcome variables were pain, physical function and morning stiffness. This study was retrospectively registered at irct.ir (Iranian Registry of Clinical Trials) with the code IRCT20220206053950N2, 2022-09-07. Results: Our findings demonstrated a significant impact of interventions on VAS score, pain, and stiffness (All, p < 0.001). Nonetheless, the effect of interventions was not significant for physical function (P = 0.78). After adjusting for the potential confounders, similar results were observed. Besides, the results of Dunnett post hoc test showed that either G1 or G3 had the most decrease in VAS and WOMAC-morning stiffness scores compared to G2 and G4. Conclusion: Based on the evidence from the present study, we can recommend a combination of quadriceps and hamstring strengthening exercises as the most effective intervention to reduce pain and morning stiffness in patients with OA.