Episode 77 | The Major Key to ACL Rehab – Quadriceps Performance

Good morning everyone, and welcome back to the ACL Athlete Podcast! I guess, I should say good morning, good afternoon, good evening, good night. It just depends on when you’re listening to this. Thanks for hanging out with me today. It is a beautiful morning here in Atlanta, Georgia. And I am pumped about this episode, episode number 77, the major key to ACL rehab: quadriceps performance. If you have heard anything about previous podcasts, ACL rehab, if you’re on social media and you’ve looked on Instagram for some people who do a lot of ACL-related work, you will not miss any type of talk about quads. We talk about quads all the time, and the quads are your quadriceps. That is the muscle that is in the front thigh between your hip and your knee. And it is the key, the main muscle in your ACL rehab. There are tons of other muscles that are important, so this is not an “or” type situation, it’s an “and.” But if we’re going to create a list or this hierarchy, “numero uno” is going to be your quadriceps. If you want to big dive into the research of why there is an episode called “Most Important Muscle In your ACL Rehab,” which talks all about the quads and why there’s research supporting it, as well as what happens when we don’t strengthen this or get the strength back. So that is a great episode to dive into if you want to learn more about this.

But today, we’re going to talk a little bit more globally or big picture about your quadriceps performance. And I think it’s such a major key in this process. I see so many athletes, whether they are pre-op, post-op, you name it, all across the spectrum. I end up seeing a lot of people who come in later because maybe they’re not getting the best rehab or maybe they need help later down the road and aren’t getting to the place that they want to get to. I can confidently say that any ACL athlete that I have seen later in this process has never had a very strong quadriceps coming into our remote coaching or into our in-person coaching. There is rarely a time when it is just at its best, it’s stronger than the other side and compared to body weight. But that’s one of the biggest constraints of this surgical process. The non-surgical process even, is the quads because of their interconnection to the knee and because we can’t extend our knee very well. There’s pain, there’s swelling, and maybe the rehab wasn’t emphasized enough in that area. 

And then what happens is, is that post-injury and post-surgery, we get atrophy. It’s just going to happen. Everyone knows it. You look down at your leg even a few days later, and you’re like, it looks like a hot dog. And you’re like, where did all of my quad go? Where’s that muscle? And it’s sometimes really hard to get back post-injury or post-surgery. And a lot of times what we’ll see is athletes will have these deficits or they will have the decrease in size that they never truly get back. Again, there could be a lot of factors. But a lot of it comes down to the rehab itself. 

A lot of times in this process, we will talk about strength, quad strength, hamstring strength, and measuring strength. And this is something that is very important. It’s the foundation of it all. And it’s where we really are able to perform and do really well as long as we have strength there, then that’s a good base. But that is not the entire picture. And today we’re going to explain why. And a lot of times you’ll see strength used in a variety of ways, different definitions. And we do have to be specific about what type of strength we’re looking at. But when people typically refer to strength in ACL rehab or especially with your quadriceps strength, we’re typically talking about that max force effort or what we call the peak torque, which we will dive into here soon. But that is typically what we’re referencing. I’m going to tell you that that is only a piece of the puzzle, a very big piece, but that’s only a piece of the puzzle in this whole process.

We are going to talk about four different qualities that make up quadriceps performance. And you need each of these qualities in order to have the best and most well-rounded ACL rehab. But if we’re talking specifically about your quads, which is again going to be the key to this entire process. Anytime I’ve seen someone get all of these pieces right, they end up having an incredible recovery. They get back to being the athletes that they need to be, and it feels really good because they feel really strong. They feel that it is similar to the other side. And so today, let’s dive into these four different qualities and we’re going to break them down based on quadriceps performance. 

Number one is quadriceps activation. Activation is pretty simple. It’s thinking about essentially that neural input, the nerve that connects into your quadriceps, your femoral nerve. And that is going to be key to getting the quad active. This is one of the things that we focus on significantly, especially post-op or post-injury. When you have the injury, the quad wants to shut down because of the pain the swelling, and other factors. But this is something where we’re looking at the activation of the muscle itself. Typically, the words inhibition or neural input will go along with it. But a great example of this could be using an EMG to see how many activations, which isn’t very practical. We see this in research. Some clinics have them, but it’s not realistic. Or practically speaking, can we get it to visually turn on and can we feel that muscle? Can we feel your quads when you do a quad set? When you go to kick on your quads, can you feel it activate, can you feel it coming on very strong and can you visually see it? It’s the same thing as thinking about whenever you go to curl your bicep or when you bend your arm to 90 degrees. If you put your other hand at your wrist and resist there, but don’t move it, you will feel your bicep kick on. And you can see the muscle belly at your bicep, and that’s what we need to see. So the same thing here with our knee and with our quad. When we go to extend, we need to be able to make sure that we can turn it on and feel it. And this is something that can be restricted, especially post-op and post-injury because of that pain that I had mentioned. 

And there’s also this term called arthrogenic muscle inhibition, or what we’re referring to as AMI, which there is tons of research and a lot of things that are coming out about this. And this is something that we’re actually going to do an entire episode on because it’s such a big factor that can linger around for weeks to months for a lot of different ACL athletes. And it’s more common than we think. And that’s one of the things that we’re playing against is this AMI. That’s where this activation and input will be key, and that’s why I also propose or recommend for every single athlete to get an EMS or NMES device, a neuromuscular electrical stimulation to help and is my go-to with any athlete, especially post-op or post-injury, who is having trouble getting their quads to kick on. So that is essentially the problem with the activation. And we’re trying to pair it up with the solution of how can we do all of these different things to get it activated. There are other things like focal cooling and all these other different possibilities. But we know that the NMES will be so beneficial to this. I was absolutely obsessed with my electrical unit whenever I was post-injury and especially post-surgery. I tried to do it as much as I could, and I just loved that I could see my quad kick on, and it helped me to be able to see it and do that mind-muscle connection and get some really strong activation, and then just hitting that consistently was really key. So activation is number one of those four different qualities we’re looking at.

Number two is quadriceps capacity. So capacity can be used in a lot of different definitions. But in this sense, we’re trying to think about the range of motion, as well as more so the repeatability or how much work can we really do. Sure, you can maybe do one knee extension, but how many knee extensions under a load can you do? And so everyone has a certain capacity or a certain threshold, if you will, that they can maybe walk a certain distance, maybe they could do a certain level of squats, they can do a certain level of pushups. And then you can go to the local, which is the different muscles. So think about your biceps. If you’re doing a really lightweight and you go to complete failure, it’s essentially testing out the capacity, or sometimes we can call it the endurance of a certain movement or muscle. 

An example of this could be either at locally, at the knee joint. We’re looking at something to test out the quads. And really the only thing we have is something like a knee extension. That’s going to be something like a seated knee extension for repetitions. You might have an ankle weight on it, you might have a knee extension machine. It depends on where the person is. But if we’re looking at locally, the capacity of the quadriceps, I like to do a knee extension for repetitions, full range of motion, no pain, feeling it in the quad, and not a ton of discomfort at the knee joint itself for higher repetitions, typically close to failure and then lower loads. We’re not trying to do a one-repetition max, but we’re trying to see the other end of the spectrum of how many repetitions could we do at a lower weight. And the weight will be dependent on you and where you’re at. But this is the local capacity. 

And then we’re looking at global capacity, which is something where we’re thinking about a bigger, maybe more compound-type movement. This could be something like a squat. One of the things I like to use is a split squat to help bias that leg, and then also put it into a position where we make sure we allow our knees over our toes a little bit. Maybe there’s a heel prop on it to be able to get into our quads, and then that way we can also assess our global capacity for maximum repetitions. I’ll say, all right, you got to do a rear-foot elevated split squat or a heel elevated split squat for repetitions on one side versus the other. Then we assess the difference to see if is it similar to the unaffected side. And then that gives us a good idea of the global capacity. And then when you’re doing the seated knee extensions, we’re looking at the local capacity of the quadriceps or really is the knee extensor mechanism, which is our quadriceps, our patellar tendons, our quadriceps tendon, the knee cap itself. It’s kind of that whole junction from your hip all the way down to where it attaches at the bottom part of the knee. And so that’s our knee extensor mechanism or our quadriceps local capacity.

I know we’re throwing a lot of terms around here, but I want you guys to be able to see this full picture and hopefully, we can help simplify this a bit. So that was number one and number two. We had number one was activation. Number two was capacity, and that’s our ability to do a certain amount of work, and that was locally at the knee with the quadriceps, and then globally with something like a split squat or something to assess more compound style movements.

Next up is our strength. And this is the one that we’re typically focusing on. And the things that we talked about previously are still going to help. Think about it as this continuum, and you got to make sure that you can get one and two before you can really get three and four that we’re about to talk about. But one and two will play into and help develop three and four. Number three is strength. Typically, when we talk about strength in our quadriceps or ACL l rehab, we’re talking about peak force or peak torque. Peak force is essentially just the amount of force that’s output. Torque is whenever that’s rotating around a certain axis. So that’s our knee and that’s typically what we’re looking at is peak torque. And that’s what these different measurements like a Biodex machine do, a handheld dynamometer. And these are the practical ways that we typically test this. And then there are other things like a one to three-repetition max to isolate the quads, like a single-leg knee extension.

This is the one where a lot of people are familiar with the term. But then getting down to the principles and understanding what strength truly is, and we’re talking about quadriceps strength. We have to make sure we understand what it is the goal that we’re working on. And we’re essentially trying to get this number as high as we can for short rep, and that’s what we’re typically looking at. We want to lift heavily in order to get this number up. It is difficult to get strong if you cannot lift heavier weights. And that’s the other downside about early post-op, is that we’re dealing with pain and swelling, a joint that’s healing. And so that can limit us from being able to lift heavy. That’s where we work on the activation and capacity. And as time goes on, based on each athlete, we are able to start working more towards strength and those higher weights and lower repetitions. 

This is probably where I see clinics and physical therapists and coaches not necessarily push athletes, or we stay in this comfortable space because we want to not hurt anyone or underload people. And then what we’ll see is that people will come into the clinic or they’ll reach out and be like, hey, I still feel like my quad is not strong enough. Or there’s a 50% deficit side to side. And it is typically because we really haven’t pushed strength and this is multifactorial. But this could be related to maybe the clinic doesn’t have any weights to push you, or maybe it’s to the skill of the clinician or the coach where they’re not really sure how to really do this specific to your knee and your ACL rehab and maybe they don’t understand strength and conditioning and that’s okay. It is just with this process, we need to make sure that we can add this in and truly work on strength. And any one of my athletes that we’re working with, they’re working on a lot of strength work. And we’re not just keeping low weights and high repetitions, we’re getting towards one repetition, five repetition maxes. And we’re making sure that we’re pushing and moving the needle forward because this peak torque or this quad strength is going to be at the base of all of these., It’s so important to get you back to all the things you need to do. And has correlated so much to people not returning to sport, to re-injury rates, to osteoarthritis down the road. This is the most important one and the most researched. But we have to have one and two in place and then really need to focus a lot on number three, which is this peak torque or this quadriceps strength. An air squats will unfortunately not get the peak up and it will not get the strength up. It has to be overloaded with lower repetitions. 

Now, let’s talk about rate; this is number four. One, two, and three was activation, capacity, and strength. Number four is rate. This is the time to get up to that peak torque. The way that I want you to think about this and this helps me kind of think about it and the way I explain it to a lot of my athletes. Is that your max strength or your peak torque that we just talked about for your quadriceps, think about the ceiling of your house. Let’s imagine you have a certain ceiling that you’re looking at, that’s essentially the peak or the maximum strength you can put out with your quadriceps with one repetition. And then your rate is the time to get to that peak. Essentially, how quickly can you get to the ceiling? Someone can take a long time to get there, or maybe they take it really quickly. There are a lot of different ways to look at this, but those are the two things that we’re mainly looking at and that actually end up accounting for a lot of the differences in our quadriceps post-ACL, injury, or after surgery. Going back specifically to rate, what we’ll call a lot of times is the rate of force development or rate of torque development, also seen as RFD or RTD. And that is again, the time to get to this peak strength or peak torque. And this is one that is definitely tough as the equipment is very important. But practically, most people do not have access to it or don’t have it at all, and that’s what can make this tough. But it’s a very important factor in this process. 

And I think with time, technology will get better. And I hope that different units will be able to measure this better. But we need a good sampling rate in order to get it. And most technology outside of ones that are thousands and thousands of dollars would not necessarily catch it. We have to figure out other ways to get it or find the equipment that can do it. This can be broken down into your eccentric and concentric rate of force development or this rate that we’re talking about. Think about eccentric as you’re lowering in a squat as quickly as you can. And then when you’re coming up from the squat, that’s the concentric as quickly as you can. We typically take these out and break them down into different pieces in order to assess them in a controlled manner. But these are the ways we think about it. Eccentric lowering or lengthening the muscle and then concentric is going to be when you’re shortening the muscle or coming up from that squat. 

And example of ways that we can measure this or look at this, is the Biodex is usually really great because you can control everything, isolate the quads, and see how quickly we can get to peak force. There are other things that you can measure to try and get time to peak force to give us a little bit of a rate of force development. There’s force plates that could be really great, but it’s hard to isolate your quad. There are things like depth jumps or even something like a vertical jump, and we’re assessing our reactive strength index or our RSIs. And then there’s stuff like banded jumps, something as simple as a wall drop to eccentrically look at this and time it. But again, this is why this process is so tough. As you can tell, the measurements for rate are a bit more difficult than the previous ones, especially strength, and it’s not studied nearly as much.

We have done some research on it. But we know that it is a very big factor. This is one area where I think the visual pieces of it can really play a massive role in helping to develop the rate. If you understand the principles of how to program and develop this for athletes and for any new ACL athletes, then that’s going to be key. And it’s not just, okay, I’m going to move this quick. Sure, that will help, but it needs to be built out a specific way, to develop this rate specifically for the quadriceps. And that’s where we need to make sure that we are able to see this really well and program it in order to develop this alongside our strengths.

It typically goes in this type of progression: the activation, number one; number two, capacity; number three, strength and; number four rate. Now, these are similar to, let’s say, for our energy system, we have our aerobic versus anaerobic. It’s not that one is completely present and the other one’s turned off. It’s almost like these sliding scales, depending on what you’re doing and what context you’re in, that you’re working on all of these. But then there’s a specific focus of whether it is the capacity or the strength or the rate. To be able to make sure we are emphasizing those areas. 

And for my athletes, we will have certain training blocks where we focus on this, and it’s usually in a very progressive way in order to develop these different qualities. I explained the analogy of the max strengthens the rate of force development. And using the ceiling versus how quickly to get there. I want you to think about this, an athlete can have an excellent peak force. This is where we’re talking about a very high ceiling. But it takes forever to get there. So that means there’s a slow rate. And this can a lot of times explain the differences in the mid to later stages where maybe someone is strong enough. Maybe they’re not moving as well, or maybe the body is not doing exactly what we’re asking it to. And it could be because they can’t get and use that force as quickly as they need to. And maybe that’s something that we need to train. And so that’s a high ceiling, but it takes a really long time to get to the top of that ceiling, and that creates some problems with our movement. Then, we have a very low ceiling. Think about literally like a basement or an attic or something where it’s really low ceiling, and then we can get there really quickly. We have a fast rate. Essentially, we have a very peak force or peak strength, and then we can get there really quickly. So that’s not really helpful either. We have a weak quad with a fast rate. The other side that I just talked about was a strong quad, but a very slow rate. And neither of these will serve us very well.

If I had to pick one, I would pick the strong quad and then work on the rate to get there. But neither of these scenarios will help us a ton. And this can be the difference between someone decelerating or landing from a jump appropriately. And let’s say, a real-time game scenario or an activity versus realistically an ACL injury waiting to happen again. And this is something that we see all the time, is that people don’t get the strength back or they don’t get the rates back, or they didn’t get coached well enough or exposed to things. And then when it comes to a real-time scenario where you are asked to do this very quickly, your body can’t produce it. And that’s where we run into trouble. This is why objective testing and being with someone who knows this process, ACLs, and the ins and outs of strength and conditioning can be so valuable in this process.

Objective testing allows us to identify the rate limiters or these deficits or gaps between where you are the ACL athlete versus where you need to be, especially in the current context of your situation. Each person is going to be very different. But the way that we anchor this is through objective testing. And then there are some of these pieces where we need a good clinical and coaching brain in order to evaluate it and be able to push these athletes forward. Don’t get me wrong, the rate of force development is awesome and great being powerful, and moving quickly, but we still need to get the whole strength piece right first. If we’re only getting 40% of the symmetry of a quad index or LSI, it doesn’t matter how quickly we can get there because it’s only up to 40%. We still have to build that base in order to utilize the rate the best. And this is the thing that I want to make sure that we drive home here. 

And credit to Dan Cobian for his work in this area. Is that when we’re in the mid to, especially later stages, we might see these deficits, but the quadriceps strength or the peak force might be there. This is typically in reference to the biomechanics, especially the kinetics that we talk about and the kinematics. The kinetics are related to the forces on the body, and then the kinematics are the motion of the movements. Think about maybe your quadriceps torque versus something like knee abduction or knee valgus is a very common one. There are the kinetics and the kinematics, the forces versus the actual motions that are happening within biomechanics in our bodies. And what we’ll often see is that the strength can get there, but we’ll still see these differences. And often that is because the rate isn’t fully there yet. And that can help explain those kinetic and kinematic changes from leg to leg. Because a lot of times what we’ll see is, oh, well, maybe they measure really well on the strength piece, but then the rate is the difference maker, and that’s what’s probably explaining a little bit of the movement side to side. They just can’t get to that peak force very quickly. And so they’re going to adopt certain movements and strategies to still complete it, but not do it the best that they can. 

So that’s why I wanted to come on here and talk about quadriceps performance specifically because what we will do is aim for strength. A lot of times in this ACL rehab process when there are different components of this we need to make sure that we nail down really well and don’t stop at strength and making sure we’re working towards our rate of getting to that peak strength as quickly as we can. But we ultimately need peak quad performance in all areas, not just the strength. If we want to get your ACL athletes ready for your sport, for your activities, for your goals, and to really and truly feel like an athlete in the way that you move. Make sure when you’re looking at this entire picture, you guys look at not only the quadricep strength, which again is so important. I can’t stress that enough. I would rather you get your limb symmetry index to 95% or 3 Newton meters per kilogram body weight, as compared to crushing your rate of force development because we know strength is protective. Get your strength there. But please look at this as a bigger picture of quadriceps performance. You have your activation, you have your capacity, you have your strength, and then you have your rate. Those four things are going to be so helpful and will help bring this full circle to make you the best athlete you could be. 

All right, team. Thanks for hanging in with me here today, guys. I’m sure, if you are a PT or a coach, this is probably a geek-out session. If you are an ACL athlete listening, you’re probably like, what is he talking about? I hope that this was simple enough to be able to understand these different components. If you have any questions at all, or if you want more clarification, I’m always game to answer some emails or messages. Send us an email, send us a message, and that way we can make sure that you have the best quad performance and, ultimately the best ACL rehab. So then that way you could get back to what you want to do. That’s all that we care about. Take care of your quads, get super strong, get super fast and powerful, and we will see you next time. This is your host, Ravi Patel, signing off.