Testing Explained: What Should Actually Be Measured After ACL Injury

Kate Sneddon

Helios ACL Project, Founder

Testing Explained: What Should Actually Be Measured After ACL Injury If you're recovering from an ACL injury, someone on your team has probably said some version of this. "We'll test you before you go back to sport." Okay. What does that actually mean? For some athletes it means a couple of hop tests. For others it means someone watching them squat and calling it good. And a lot of athletes get through most of ACL rehab without ever having their strength measured at all. That gap is exactly why I built the Helios ACL Testing Network. Objective ACL testing should give you real data about what your body can do. Not a vibe. Not an opinion about how your knee looks. Data. And the place to start is strength.

What Does Objective ACL Testing Actually Mean? Objective testing means measuring something in a way that produces a number. A number you can track, compare, and actually use to make decisions. Instead of "your quad looks pretty strong," we measure how much force your quad actually produces. Instead of "your jump looks good," force plates show us how you produce and absorb force when you land. That difference matters more than people think. ACL recovery takes a loooong time. Sometimes years. You need better information than a calendar. You need to know what's improved, what's still behind, and what needs more work this week. That's what testing gives you.

“ACL recovery takes months. Athletes need better information than simply knowing how much time has passed since surgery.”

Why Strength Testing Is the Foundation of ACL Recovery Every Helios Testing Network location is built around one non-negotiable: objective strength testing. After ACL reconstruction, quad strength is one of the most important things we can measure throughout your recovery. But it has to actually be measured, not estimated. Squats, lunges, step-downs, single-leg work. These tell us useful things about how you move and what you can tolerate. They do not tell us how much force your quad can produce. Only a real strength test does that. That's why every Testing Network location has equipment built for this. Depending on the site, that might be a dynamometer or an isokinetic machine. The equipment can vary. The ability to collect reliable strength data cannot.

What Can Quad Strength Testing Tell You? Strength testing gives you numbers you can follow through every phase of ACL recovery. You can compare your involved leg to your uninvolved leg. You can track whether your involved leg is getting stronger between sessions, not just staying the same. You can look at strength relative to your body weight. And you can use all of that to figure out exactly what needs to move to the front of your training plan. That is a completely different conversation than "do your legs feel even." Which brings us to the number almost every ACLer has heard and almost nobody has had explained properly.

What Does 90 Percent Limb Symmetry Actually Mean? You've probably heard your surgical leg needs to hit 90 percent of your other leg. This is called Limb Symmetry Index, or LSI. If one leg produces 90 units of force (let's say in pounds for this example) and the other produces 100, you're at 90 percent. Useful information? Yes. The whole picture? Not even close. Here's the problem. Say both legs got weaker in the months after your injury. Your surgical leg produces 42 lb. Your other leg produces 46 lb. You're 91 percent symmetrical. That number looks great on paper. It tells you nothing about whether either leg is actually strong enough to do what you're asking it to do. I have seen this exact scenario play out with real athletes, more than once, especially with female athletes whose strength numbers get compared to a "normal" that was never high enough to begin with. Someone gets told "you hit 90 percent, you're good," when their actual force output relative to their body weight is nowhere near enough. Symmetry alone is not a return to sport clearance. It's one data point. If your team is only asking "how similar are your legs," they're not asking the right question. The right question is "how strong are you to be safe when the going gets tough"

“If your team is only asking "how similar are your legs," they're not asking the right question. The right question is "how strong are you to be safe when the going gets tough"”

What About Force Plates Testing During ACL Recovery? Some Testing Network locations also offer force plates. Force plates measure what happens during jumping, landing, and hopping, not just the outcome of the task. Instead of only knowing how high you jumped, force plates can show force production, impulse, jump strategy, landing strategy, and side to side differences. That's another layer of information on top of strength testing. But here's the distinction that matters: force plates are valuable, and they are not required to objectively measure strength. A location without force plates can still give you real, usable data if they have proper strength testing equipment.

Do All Helios Testing Network Locations Offer the Same Tests? No. Some locations have dynamometry. Others have an isokinetic dynamometer. Some also have force plates or timing gates. Instead of forcing every provider to buy the same equipment, the Network sets one baseline: every listed provider has to be capable of collecting reliable, objective strength data. Beyond that baseline, you can look up any location and see exactly what additional testing they offer before you book.

When Should You Get Tested During your ACL Recovery? Not just at the end. That's the biggest misconception out there. One of the best things about testing is that it shows you change over time. An early test tells you where you're actually starting, not where you think you're starting. A later test tells you whether your training is doing what it's supposed to do. Test. Train. Retest. Adjust. That's the loop. Treat testing like one pass or fail moment at the finish line and you lose the entire point of collecting the data in the first place.

Is ACL Testing the Same as Being Cleared for Sport? No, and this distinction matters. A strength test, even a full testing session, is one piece of information inside a much bigger return to sport decision. Your surgeon, your PT, your strength coach, whoever is on your team, they're all weighing other factors depending on your injury and your sport. The Helios ACL Testing Network was never built to promise that one session tells you if you're "safe." It was built so you have access to real information that your team can actually use to make that call.

What If My Physical Therapist Doesn't Offer This Testing? You don't have to leave them to get this. That's actually the entire point of the Network. Find a Testing Network location, get objectively tested, and bring those numbers back to the people already running your recovery. Every provider in the Network is expected to collaborate with your existing care team, not compete with it. This isn't about collecting your case. It's about collecting better data so you can advocate for yourself with real numbers instead of a guess.

Find ACL Testing Near You If you're recovering from an ACL injury and nobody has objectively measured your strength yet, or you're overdue for a retest, use the Helios ACL Testing Network to find a provider near you. Search by location, see exactly what equipment each site has, and find the option that actually fits what you need right now. You're allowed to ask for real numbers. Go get them.

“Testing shouldn’t be one giant PASS/FAIL moment at the end of ACL recovery. Think of it as a series of checkpoints.”

Kate Sneddon, Helios ACL Project