10/20/2026
Your good leg isn't automatically the standard.
Limb symmetry testing compares your injured side to your uninjured side. It's a useful check, and it belongs in a return-to-sport battery. But it only works as well as the leg you're comparing to.
After an injury, the "good" leg often gets less load, less sport, and less training, so it can slip too. That part is clinical reasoning. Here's what the research adds: in one study of 70 athletes tested 6 months after ACL reconstruction, 40 reached 90% symmetry on quad strength and every hop test, but only 20 reached 90% of their estimated pre-injury levels (estimated from the uninjured leg's pre-surgery numbers). One study, so not the final word, but a good reason not to treat symmetry as proof of readiness.
A better approach is more than one reference: pre-injury numbers when you have them, typical numbers for your sport and size when you don't, and the actual demands of your sport.
If you're in late-stage rehab, ask what your results are being compared to.
Follow for more of the details that are easy to miss in return-to-sport testing.
Source: Wellsandt E, Failla MJ, Snyder-Mackler L. Limb symmetry indexes can overestimate knee function after anterior cruciate ligament injury. J Orthop Sports Phys Ther. 2017;47(5):334-338.
