Intro: Welcome to UAB MedCast, a continuing education podcast for medical professionals, providing knowledge that is moving medicine forward. Here's Melanie Cole.

Melanie Cole, MS (Host): Welcome to UAB MedCast. I'm Melanie Cole. And today, we're talking about ACL injuries, gender disparity between female and male athletes and reducing injury risk. Joining me is Justin Kirk. He's the lead physical therapist at UAB Sport and Exercise Medicine. Justin, thank you so much for joining us today as we're talking about gender disparity between female and male athletes. Female versus male risk for ACL injury is such a hot topic in all of Sports Medicine right now. We've been talking about it for a few years. And people are saying that females, larger Q angle created by having that wider pelvis could be one of the causes. Can you speak to that a little bit and why you feel that girls are more susceptible to ACL injury than boys?

Justin Kirk: Yeah, that's a great starting question. And, you know, it's one of those things that the Q angle has been perpetuated for years. And recently, some of that research validity has been shown to be less of a factor. They've done some studies where they take Q angle measurements on female athletes preseason and have shown that it's not a good predictor for who will end up tearing their ACL.

What actually is a good predictor is the dynamic knee valgus. So during a movement, like a landing from a jump or a cut at high velocity, how much can you control the knee is more of an indicator than just the Q angle in a static posture. And it is one of those things that is painting with too broad of a brush because every female athlete would tear their ACL all the time if it was just Q angle because of the anatomical difference. So, to blame it on the Q angle seems far too simplistic, especially with our current understanding.

Melanie Cole, MS: I completely agree with you. That was an excellent explanation. So, hormone differences have also been mentioned, you know, if it's post-pregnancy, they're relaxing. And can you give us any indication about hormone differences and where we stand on that as of now?

Justin Kirk: I think this is one of the most emerging aspects of the research for ACL and gender disparity. And that is because the evidence right now is conflicting. It's not a hot topic if there's clear evidence. And so, there needs to be better data. There is certainly mechanistic ideas of why, but does that play out in real time? And currently, because the evidence is mixed, I tell people all the time, "Hey, females are smart. If it was a simple causation, they would've figured it out." Females would get together with their other friends who've torn their ACL and say, "Hey, you know, I was at this point in my cycle. These injuries are all happening at the same time," they would've figured out a long time ago. But because the data is still conflicting, FIFA this year announced that they would fund a long, multi-site study, investigating with blood work to kind of show where these injuries are happening within the cycle and kind of plot it against lots of different female soccer athletes. And most of that's happening over in the U.K. And so, we'll see, hopefully, within the next year or two when that data emerges what's actually happening, with the hormonal cycle.

Melanie Cole, MS: So if we've mentioned hormones and we've mentioned that Q angle, do you have any other theories yourself, Justin, about why you think that there's really such a disparity here?

Justin Kirk: Yeah. This really gets me fired up, because I do see a lot of female athletes and I'm a dad of two daughters. And there's this research study that came out a few years ago called a gendered approach to ACL management. And it's essentially saying that we want to talk about the gender disparity. We really have to talk about what is happening as we manage young female athletes and young male athletes.

And if you look at the graph of intensity over time, it's a little difficult to imagine over a podcast, but I'll kind of describe. Young males and female athletes, as they enter high school, their training intensity background is about the same. So, the slope of the line is about the same. But in early high school, male intensity training minutes increase, the volume dramatically increases, and females do not increase at the same rate. So during that critical period, the slope of intensity minutes as their body is developing through puberty is not equal. And part of that is access to strength training. Part of it is the societal norms and the desire to not get bulky and some other things that we have to better support and coach young female athletes through. But we know not only are males getting more intensity minutes earlier in terms of strength training, conditioning, things like that, but also females go through puberty earlier. So, they need it even more so, right? So, the disparity is there's this large gap between they're not getting what they need and they're going through puberty faster and earlier than males, and that's creating the gap.

Melanie Cole, MS: So, let's talk about the injury themselves, Justin. Do we look at this as a biomechanical injury? Are there other tertiary considerations? Tell us a little bit about the injury when it happens. And when they come to see you, what are you seeing?

Justin Kirk: I think strictly from a mechanical perspective, they've taken cadavers and measured the force that it takes to tear the ACL. And obviously, it's going to be more than that in vivo. But they've shown about 500 pounds of force in a cadaver, which we know that when we run and jump and pivot at high speeds with sports, we're experiencing forces that are two to eight times your body weight. So, it doesn't take a lot of complicated math to realize you can very quickly, generate 500 pounds of force in a full-grown human. And so, that's not a one-for-one causation where it's just strictly mechanical. But part of it is this neuromuscular component, right? Where it takes about 30 to 50 milliseconds to tear an ACL, and it takes about 200 to 300 milliseconds to reach peak voluntary muscle contraction. So, that is how fast you can reach your maximum force output voluntarily compared to that 30 to 50 milliseconds is how much your body can react and adapt without even thinking subconsciously. So, there is that component that's mechanical. And then, there is that component of we need to be doing some things to improve rate of force development and rate of force acceptance if we really want to impact our outcomes.

Melanie Cole, MS: Well, that's certainly true. So as we look at coaches, providers, when they're working with athletes that are at a higher risk, what do we want to do with our young athletes to reduce that risk for ACL injury? Speak a little bit about some of the training techniques that you recommend, whether we're talking plyometrics or lateral training, any of these things that you work with coaches and other providers to help control that risk.

Justin Kirk: Last month, I spoke at the state conference for the state of Alabama Physical Therapy Association. And I put a Venn diagram on the slide. You know, one circle is strength, one is neuromuscular, and one is the neurocognitive component. And we have to address all three things, because we are a complicated human movement system. In the past, they thought, "Oh, we'll just do some hamstring exercises, because the hamstring can decelerate the tibia and act as a parallel force to pull back on that ACL. We'll do some lateral strengthening stuff to help with the hip rotators and the hip abductors. And those things are all valuable." But if you're not doing the neurocognitive and neuromuscular component like plyometrics, like lateral agilities and getting those exposures, even with adding some contact. So as a part of the drill, you could have some gentle contact from a teammate or a coach to kind of simulate some of those environments.

But you want to do all three items in the Venn diagram, right? You want to do strength, you want to do neuromuscular control, which is control that dynamic knee valgus. And you want to do the neurocognitive component, which is how fast can you subconsciously develop force and absorb force. Because at the end of the day, it is the equation of you versus gravity and momentum, and how does your body absorb that force.

Melanie Cole, MS: So, speak about limb symmetry and single-leg training and where that fits into this Venn diagram you're talking about.

Justin Kirk: Surely that goes directly into strength. And, you know, in the past, they thought quad strength, symmetry and hamstring ratio would be a great predictor. But unfortunately, it is not a great predictor. It is still valuable, but it's just not going to predict who will tear and who will not tear an ACL.

And I think we should always strive for symmetry. But again, that has not been indicated in healthy populations as a like one-for-one ratio of who will tear. Just because most athletes, say in basketball, if you're a right-handed athlete, you're not going to be jumping off both legs equally. And then, in soccer, you know, if you're primarily kicking with one foot, you're going to be planting on that left leg if you're a right-foot kicker a little bit more, which means left leg is going to absorb a little bit more of that plant force. So, you've got to take that weight room, strength symmetry into practice and figure out how do we coordinate movement and the strength that you have to control the forces of gravity and momentum.

Melanie Cole, MS: This is really such important information, and we're learning so much more. And Justin, as we think of the changes in management of ACL tears over the past, I don't know, five or 10 years or so, speak about some of those changes and also how return to play is determined after this injury, because as they're more common in women, are they more likely then to re-tear? And how are we looking at return to play?

Justin Kirk: Yeah. And again, you know, if people don't do the physical therapy and proper return-to-sport testing, re-injury rates are about one in three depending on the study. You're looking at 25% to about 38%, which if you look at the middle of that, it's about, you know, one in three. But the reason why I'm so passionate about the ACL is if people do a great job with physical therapy and they do the return-to-sport testing, you're pulling that ratio down to less than 10%, sometimes 3-5%. But on average, about, you know, 6-8%.

So, you can really dramatically improve people's outcomes. If you do a great job with the nine months of physical therapy and you don't let people return to sport at the high level without restrictions until they pass, the research-validated tests, which now we are adding more and more to the battery because we realized, again, simple strength symmetry does not let you know how people are moving. It lets you know their strength output, but it doesn't let you know what the quality of the movement is. And historically, we've done hop testing in a forward hop manner. But now, we're adding tuck jump assessments and backwards hopping and hopping onto force plates and some other things like that. But really, what you're trying to do is just get a picture of how strong the individual is. Can they withstand the forces that we want them to withstand? And then, how well do they move? Do they move in a way that is safe to return to sport in a closed environment in a clinic, right? Because once they get out there in an open environment with distractions and other players, they've got other things to consider, right? So if they can't pass these tests in clinic, then we're really not feeling great about them going back out there.

And, you know, same thing with the hop testing with our traditional four hop tests, the calf and the glute get to participate in propelling you forward during those hop tests. Up to one-third of the force can be from the glute and up to a third of the force can be from the calf. So if you can't pass that, then you've really got no reason to be out there, which is why we're adding some of these other tests.

Melanie Cole, MS: As we wrap up, Justin, when we think about prevention, which is really the goal here, and that's really what we're looking for to reduce the risk of these ACL injuries in women, I'd like you to give us the key takeaways, what you want people to understand about the gender disparities and reducing that injury risk between female and male athletes when it comes to ACL injuries.

Justin Kirk: I think at the end of the day, it's not a quick fix, which stinks. You know, we want to make a difference now, but we've got to intervene earlier when these females are developing and going through puberty and we've got to change societal expectations to show, "Hey, once you get to college, if you want to pursue college athletics, all of these ladies that are competing at the high level are lifting." So, we're not going to get bulky. We're not going to get any kind of these negative associations that society puts on strength training for young ladies. And we have to support them from access to fields, access to coaches, access to strength and conditioning coaches. We've got to have females who want to be strength and conditioning coaches and be young role models for these girls who they look up to these strength and conditioning coaches and say, "Oh, hey, she values lifting and she's not bulky. And therefore, I can see myself doing that." So, we really have to change the environmental and societal and kind of cultural expectations around what we're doing. And part of that is birthed out of the fact that up until very recently, they thought that any strength training for youth athletes was not okay. Because they feared that it would affect the growth plates and other things. But kids are jumping out of trees and they're playing these sports and they're tearing the ACL, which means they're already exposed to these high levels of force, they might as well learn how to do it safely.

Melanie Cole, MS: So important what you just said, to bust up some of these myths and misconceptions that we've had over the years about youth and strength training, and women and strength training. Certainly, there's plenty of misconceptions to bust up there. But, Justin, thank you so much for joining us today and really sharing your expertise. And for more information, please visit our website at uabmedicine.org/physician. That concludes this episode of UAB MedCast. I'm Melanie Cole. Thanks so much for joining us today.