Anterior cruciate ligaments (ACL) injuries account for a significant proportion of all sports-related injuries. Despite successful completion of a rehabilitation program, about 35% of ACL patients experience re-injury after return to sport, and studies have identified persistent quadriceps strength deficits as a potential cause [1–3]. Deficits in quadriceps strength can be monitored throughout rehabilitation using muscle strength testing. The most common test protocol involves isometric testing of quadriceps strength whereby the knee is extended against a static resistance. In this method, the clinician uses their strength to resist the patient’s motion and subsequently assigns a qualitative value of strength. The highly subjective nature of this test has motivated clinicians to use devices that can more accurately assess quadriceps strength.

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