Episode 261 | The ACL Is a Seatbelt: You Don’t Know You Need It Until You Do

What is up team? And welcome back to another episode on the ACL Athlete Podcast. I hope you guys are doing well, and I hope that your week is going well. I know that this crazy arctic blast across the U.S. has been a little crazy for folks, especially for those who are not so prepared for ice, snow, and cold weather. I hope everyone is doing well out there. If you don’t know what I’m talking about, it’s probably way past the time of you listening, or it’s just not relevant to you. But for those of you who are listening, I hope that you are doing well.

Diving into today’s topic, what if I told you that most athletes don’t actually know when they need their ACL? I mean, who does? There’s a bunch of different ligaments in the knee. There are a bunch of different supportive structures, which are the muscle groups. Those are active, and then there’s passive structures, which are typically your tendons and your ligaments, especially your ligaments. Different things essentially make up the knee joint itself, and the thing that supports its stability. And athletes, when they need their ACL and don’t need their ACL, you’re not really gonna notice it. Not when they’re walking, not when they’re lifting, not even when they’re jogging or potentially even cutting lightly or doing more rehab-specific drills, especially because it’s all submaximal.

Now, don’t get me wrong, there are situations where you step off of a curb if you don’t have an ACL and that knee gives out. And I went a good long period of time because of insurance issues for my first ACL. I basically walked around for a few months without an ACL. I got pretty familiar with how the knee felt and tried to do things, and I was able to get back to doing a lot of daily stuff, moving stuff, lifting stuff. And then I tried to test it out for a run one time, and I hit a hard cut because I was also in high school and didn’t know any different, honestly. And my knee shifted. And so then I was like, oh, that’s why I need my ACL. But the thing is, because the ACL doesn’t just really announce itself, that’s the thing about this process and the knee itself. It’s more, what I like to say, it’s more like a seatbelt. You don’t feel it doing anything until the exact moment you desperately need it.

Today, I want to talk about why feeling good, especially in ACL rehab, late in the process, can actually be one of the most dangerous phases. Take that for what it’s worth. But I do think that there is some merit to this because of just working through this process, and this process taking a long time. I want to dive into that. Also, why clinical exams and timelines can give false confidence. And why objective testing is the only way to really know where the knee stands, especially as time goes on. 

In terms of the seatbelt analogy itself, let’s pause for a second and address this head-on. Does the seatbelt analogy actually make sense for the ACL? Absolutely. And from a biomechanics and a real-world risk standpoint, it’s actually a very strong analogy in this. Because the ACL itself is a largely passive structure until a high-risk event. It’s not heavily stressed in low-speed, controlled tasks. Its true value shows up in unexpected, chaotic, high-load moments, those high-stress moments. Because you don’t feel it’s protecting until it really fails, honestly. It’s either tearing or it’s not there.

Most importantly, the “absence of symptoms does not equal the absence of risk.” I think that is something that can be really challenging. And this is exactly how a seatbelt works. I was trying to work this out in my head in terms of like, okay, does this actually make sense? I’ve just been thinking about it more in terms of the seatbelt that’s there. You can really drive for years, feel totally fine, never think about having your seatbelt on until there’s one moment where it suddenly matters more than anything else. And that’s the way the ACL essentially functions the same way. Most of what we do in rehab, even some of the advanced rehab, if you will, doesn’t fully stress the ACL. You’ve got to think about when you’re straight line walking, controlled lifting, right. The predictable single-leg work, especially gym-based work, you’re not going to really be testing that ACL out as much. Now, it can feel like that ACL is super fragile. It’s healing in there; if I do any sort of movement, it’s going to give. And there are different phases of this where this matters, depending on the healing of the ACL.

But most importantly, the stability and the structures around the knee, most importantly, the muscle groups. Whenever the quad is not turning on, then yeah, we might actually have to resort to other passive structures in the knee. Because when you go to do something and that muscle group isn’t helping do its job, then we do rely on the passive structures. Right, because those things are going to work if the other muscle groups are not strong enough or they’re not kicking on enough to be able to provide that additional active stability, which is the primary focus of what’s gonna protect the joint. And so with predictable single-leg work, you’re not going to really notice it. Even pre-planned, like change of direction stuff, you know, those are things that you’re probably not going to nearly notice that knee giving way as much as in your brain you might think. These are very low chaotic environments and probably sub-maximal. What I mean by this is not a hundred percent intensity. 

Athletes start saying, I don’t even notice my knee anymore, it feels normal, I feel strong, right. And that makes sense, right, because you’re going through this rehab process. Most of the time, especially in rehab, you’re not necessarily testing the car at a hundred percent speed. Therefore, you’re not really gonna notice the seatbelt effect of it. Now, there can be those episodes where it gives out when people don’t have their ACL. But that’s the thing that can always be challenging in this process because the ACL’s job isn’t to protect you in just like these clean, predictable situations. Its job is to protect you when you decelerate late, react instead of planning the situation, maybe you land awkwardly, you’re tired, and fatigue plays into this. And then of course, the environment is chaotic. You are really testing out that knee. And you’re having to react to a lot of different things. You don’t know if the system is ready for that by “feeling good.” And that’s the thing that’s really important here. 

Feeling good to me can be a big disguise. And it can be challenging in ACL rehab. This is where things can get really hard and even potentially a little dangerous, if you will, because as time passes in this ACL process and after surgery, the pain starts to typically get better. The swelling decreases. Movement feels easier. And typically, people’s confidence also increases. And so then, eventually, the athlete will assume I must be good to go at a certain point in the process.

But the symptoms disappearing does not necessarily mean that capacity has been returned, and that’s super important here. And I think sometimes because things feel good doesn’t necessarily mean that their strength, power, or ability. All the muscle groups and surrounding tendons need to work together to be able to perform. Doesn’t mean that it’s been met yet. Under the surface, you could still have those quad strength deficits. You could have a poor rate of force development. If you’re thinking about strength, we’re talking about how high a ceiling you can produce the force. And then the rate of force is essentially how quickly you can get there. In sports and activities, we want to be able to access that strength very quickly. If we’re super strong, but if we can’t access it quickly, especially when we have only milliseconds to react, it’s not really helpful. So that’s why we also have to work on the power rate of force part of this process. 

The other thing too is that asymmetries masked by compensations have really played a big role in this process. Because you think about how long you go with the injury and then also the post-op process, if you go that route. Your body has learned ways to work around this to be able to get the job done. To take the stairs, to walk, to be able to even sit down in a chair, and even to lift. Asymmetries are all over the board with any type of injury because our body finds a way to get it done.

Poor tolerance to fatigue is also something that we will see based on this inadequate deceleration capacity. Being able to brake and slow yourself down. And then reactivity, there can be some gaps in this that never really show up in the typical strength standard rehab. And especially if rehab for you was too conservative, avoided uncomfortable loading. Didn’t necessarily progress speed, chaos, or fatigue. And then focused on completion instead of the stress exposure of this process. It is challenging because when you think about most physical therapy clinics, they’re not equipped to be able to take on this full process. But again, when we’re looking at certain healthcare models, insurance models, people are typically going to these clinics for months and months on end, and hoping that it can get them there. 

Now, don’t get me wrong, there can be limitations to so many clinics. Because not everyone has just this turf and an open free weight room to be able to do everything. But I think we need to know the limitations of that. So you’re going to be limited by the environment you’re in. For example, if you have a sports car and you are driving in a neighborhood, you are never going to test the limits of that sports car. And just know that you’re never going to get it up to a hundred percent of its capacity because the neighborhood is built a certain way. You have turns. You have cul-de-sacs. You have roundabouts. You have tons of stop signs and speed bumps. You’re never gonna hit full speed in a neighborhood. And that’s the same thing with certain rehab environments, if I’m honest. Most of the time, we can’t necessarily open it up and be able to test how you’re doing on a field or on a court. Or to be able to cut, jump, and express yourself with high velocities. We need to know the limitations of that. Therefore, if we can’t necessarily test it, then we’re not necessarily going to get that ACL up to a certain point.

Now again, we’re not trying to test it to failure. We’re just trying to make sure the exposure is there. And that way you’re not mistaken by whatever you did in the small clinic. Thinking it’s going to necessarily keep you fully protected. Because you are limited by the constraints of the clinic. The thing is, you just don’t find these gaps by accident; you only find them if you actually look for them. And that’s the biggest thing here. 

One of the other things I do want to discuss here that aligns with this, essentially, the clinical exam is a challenge. It’s a problem. I don’t think this gets said enough. But you know when a surgeon examines your knee in a quiet clinic. It’s in this small room that you sit at the table. You lie back. They’ll do the Lachman test. They may do the pivot shift test. You’ll sit up, and then they’ll kind of put their hand on your ankle and kick out into it. They’ll look at it, and they say, yeah, that ACL is in there. It’s strong. The ligament’s there. It just means the ligament’s there. They can’t tell how strong the ligament is. They don’t know its capacity. You know, the graft is intact, the ligament is there. That is really all that they can tell you based on that. Especially in that five to ten-minute time period they take with you. And so the thing is that this is not sufficient for a clearance. And it’s not sufficient to just let us know, like okay, now you can move forward with X, Y, and Z. It’s usually based on timelines that they use. And also just that five-to-ten-minute test or time with you, if you will. 

The exam itself doesn’t tell us how you absorb force. It doesn’t tell us how quickly you can produce force. It doesn’t tell us how your knee behaves under fatigue. Whether you rely on compensations that you can’t necessarily feel. And as much as everyone says, like I don’t compensate. Or I feel like I’m doing it equally. If you check out Susan Segward’s work. She has an incredible study talking about being able to look with the naked eye months post-op ACL. And you can’t see any differences. But when you look at the muscle activity, there’s a shift early on; you shift to the uninvolved side. And then as time goes on, you start to shift to the involved side. But you start to move your focus from the quads to the hamstrings and the calves. The body is an incredible master compensator. And I’ve seen people look so pristine in terms of their movements. And the thing is that sometimes they’ll be like, yeah, I don’t really feel it there though. 

Our job in rehab is to constrain things so they have no choice. That’s why we love the knee extension machine. Because you have no choice but to use your quads. But with that said, the visual or the qualitative assessment with a movement is important, but it’s not the only thing. We have to make sure it matches up to an objective component. The main thing I want to point out here is why this matters more the further out you are. 

Now, early on, you know, the first three to six months or so. People are like, I’m still in it. I know I’m not there. They’re still healing. Once people start getting into that eight- to nine-month process, especially a year mark, they start to think about things a little differently, especially because you’ve been in it for a while. And again, there are so many people across the spectrum. We have athletes who are way over this. Who have come to us much later in the process. And they have a humble understanding of this. There’s some people who honestly just don’t know any better. Or it’s just really challenging because it’s a little bit of a paradox. The later you are in post-op, the harder it is to tell if something is missing, unless it’s super obvious. Early on, pain gives you that feedback. The swelling limits some of the behavior. And then of course there’s guarding. 

Later on, it’s probably more common to say that people get months out. That their pain is better. Their swelling is typically better. They’re guarding less. They’ve gotten used to things. They’ve gotten stronger. So their movement feels free. You’re trusting the knee a bit more, and you stop questioning it as much. Your sport doesn’t care how long it’s been since surgery. It cares whether your knee and your body can handle force, speed, timing, fatigue, and chaos. That’s why so many re-injuries happen when athletes say, “I felt totally fine.” You don’t realize you need the seatbelt until the crash happens. And that’s exactly why objective testing exists—it’s how we check the seatbelt before real life does.

Objective testing isn’t about fear. It’s about verification and validation. It tells us whether the body can meet the real demands of sport, not just daily life. Whether it’s skiing, soccer, handball, MMA, climbing, or any high-demand activity, the knee has to be prepared for those forces. Testing answers questions that feeling alone cannot answer. Can you actually produce enough force? Can you absorb it quickly enough? Do asymmetries show up under load? What happens when fatigue is introduced? Does your performance match the demands of your sport? Testing doesn’t mean something is wrong—it means you’re checking the system before the system gets checked for you.

If you’re an athlete, parent, coach, or physical therapist, feeling good matters, confidence matters, and time matters. But none of those replace evidence. The real question isn’t “does my knee feel okay?” It’s “Is my knee ready for the worst-case scenario?” Sport isn’t going to ask for permission, and the ACL doesn’t usually fail in rehab—it fails in real life. You have to test-drive the system. And the only way to know if you’re ready for real life is to test it like real life is coming. That’s why criteria matter, and why feeling alone is not enough. The ACL is the seatbelt—you don’t want to find out it wasn’t ready when it’s too late. ACL rehab is not a process where “good enough” works. Being at 70% or 80% isn’t enough, especially late in the process. Research consistently shows we need to be within about a 10% deficit, with context based on goals and sport. Feeling close is not the same as being ready.

A major problem is how clearance often happens. Many athletes are cleared based on timelines and quick clinical exams. Some surgeons do comprehensive testing, strength measures, and movement analysis—but they are the exception, not the rule. Too often, athletes are told to “ease into it” without true field testing, jump testing, or fatigue-based assessment. I’ve seen this firsthand with youth athletes who still have large quad deficits but are cleared anyway. Telling someone to ease back into a collision-heavy sport with a 30% deficit is not enough. With re-injury rates as high as they are, that approach is simply too risky.

As an ACL community—athletes, PTs, coaches—we have to do this better. Make this the last time you go through this process. Test it properly, because the ACL is something you don’t realize you need until the moment you do. Yes, we care about how you feel. But we also need objective testing that’s valid, evidence-based, and data-driven. Feel becomes more misleading the further out you are from surgery, and that’s when risky decisions get made. Don’t be one of those people.

I hope this helps. Until next time, this is your host, Ravi Patel, signing off.