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Objective: The main objective was to evaluate the anterior flexion force (AFF) and the lateral abduction force (LAF) of patients who underwent reverse shoulder arthroplasty (RSA) and to compare the measured force with that in a similar-age control group. The secondary objective was to identify prognostic factors for muscle strength recovery., Methods: Forty-two shoulders that underwent primary RSA between September 2009 and April 2020 met the inclusion criteria and were called the arthroplasty group (AG). The control group (CG) consisted of 36 patients. The mean AFF and the mean LAF were evaluated with a digital isokinetic traction dynamometer., Results: The average AFF found in the AG was 15 N, while in the CG, the average AFF was 21 N ( P  < .001). The average LAF in the AG was 14 N (standard deviation [SD] 8 N), while in the CG the average LAF was of 19 N (SD 6 N) ( P  = .002). All prognostic factors studied in the AG showed no statistical significance: dominance (AFF 0.697/LAF 0.883), previous rotator cuff repair surgery (AFF 0.786/LAF 0.821), Hamada radiological classification (AFF 0.343/LAF 0.857), magnetic resonance imaging (MRI) pre-operative evaluation of the quality of the teres minor (AFF 0.131/LAF 0.229), suture of the subscapularis at the end of the arthroplasty procedure (AFF 0.961/LAF 0.325) and postoperative complications (AFF 0.600/LAF 0.960)., Conclusion: The mean AFF was 15 N, and the mean LAF was 14 N. The comparison of AFF and LAF with a CG showed a 25% reduction in muscle strength. It was not possible to demonstrate prognostic factors for muscle strength recovery after RSA., Competing Interests: The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article., (© The Author(s) 2023.)