Current concepts and future perspective of muscle function tests to inform return to sport decision-making after ACLR: A narrative review.

An injury to the anterior cruciate ligament (ACL) can be sustained in sports participation during situations such as offensive cutting, landing from a jump, or defensive pressing. Despite treatment with surgical reconstruction and/or rehabilitation, only 55%-84% of patients return to sport (RTS) after treatment, and second ACL injury rates remain as high as 25% in young athletes. To reduce the risk of second ACL injury, clinicians commonly use muscle strength tests, hop tests, and patient-reported outcomes (PROs) to evaluate readiness for RTS. These tools have become central in clinical decision-making, yet significant challenges remain. Current tests typically rely on limb symmetry index (LSI) thresholds, with ≥90% LSI commonly recommended as a clearance criterion for RTS. However, these cut-offs have shown poor predictive value for second ACL injury risk and may be misleading. The LSI also fails to account for pre-injury strength, bilateral deficits, or compensatory movement strategies. Hop tests provide additional insights into explosiveness and load absorption but emphasise distance or repetitions rather than movement quality, missing key biomechanical risk factors. Similarly, while PROs aim to capture the psychological dimension of recovery, they cannot be used in isolation to determine readiness for RTS. Collectively, these evaluation tools provide only snapshots of recovery and do not adequately reflect the chaotic, multidimensional demands of sport. The research gap lies not in the absence of tests, but in their limited transferability, standardisation, and contextual relevance. Current tests should not be viewed as a simple pass-or-fail clearance point, but as guidance for informed decision-making in rehabilitation. Continuous evaluation across physical and psychological domains can help clinicians tailor progression, motivate patients, and support safer transitions toward sport. This narrative review explores the current state, limitations, and future directions of RTS testing in order the bridge the gap between clinical measures and the chaotic, high-demand realities of sport. Level of Evidence: Level III.