By Jordan Smothermon
Female adolescent athletes are three times more likely, on average across all high school sports, than their male counterparts to suffer an anterior cruciate ligament (ACL) tear. The severity, cost, length of recovery, and emotional and mental toll ACL tears (and other knee injuries) take on young, developing athletes provide considerable and compounding reason to reduce the risk of such injuries, especially over the long term.
Females are more susceptible to knee injuries due to a confluence of anatomical and neuromuscular factors. Since anatomical factors are largely fixed and unalterable, we’ll focus on listing and improving the neuromuscular factors. In essence, adolescent girls use their muscles differently than boys to control their bodies. Girls are quad dominant, meaning they use their quads to control knee motion. Boys, on the other hand, tend to use quads, hamstrings, and gluteal muscles to control knee position. Theses muscles working together reduce strain on the ACL. By being quad dominant, girls are more likely to pull their shin bones forward away from their thigh bone – the very thing the ACL is resisting – thereby straining the ACL.
Girls also tend to have one leg stronger than the other, meaning that one leg will support more weight than the other, leading the unweighted leg to shift into a bad position as the center of mass moves away from an even base of support. Weaker core strength can also lead to ACL injury in the same manner since a weak midsection reduces control over limbs, and can again lead to a center of mass that isn’t over the base of support, meaning, hips aren’t inline with knees that, in turn, aren’t over feet.
Finally, girls are more likely to rely on bones and ligaments to stop joint motion than boys are. For example, a girl is more likely to allow her ankles to dive in which leads to her knees diving in. When her knees and thighs hit together, it is this bone-resting-on-bone action that stops her knees from moving rather than relying on the work of her quads, hamstrings, and gluteals to stop the knee motion.
These neuromuscular factors leading to ACL injuries can be trained (or, retrained) to reduce injury risk.
A number of training programs exist designed to do just that. These programs tend towards using drills and exercises to increase neuromuscular function, employing low-level plyometrics, simple bodyweight-only strength, shuttle drills, and bilateral and unilateral jump work. These comprehensive practices display effectiveness in reducing knee injuries according a number of studies. Largely, these practices must be maintained continuously to reduce injury risk. Therefore, their long-term efficacy is unknown. It makes sense that if an athlete continually works to improve neuromuscular function, then they are more likely to permanently integrate the proper function. However, limited data exists to verify this long-term adaptation.
Moreover, few published and/or easily accessible plans contain resistance strength work (strength training using weights). None of the most popular plans contain resistance strength work. Many of the plans use short, 20-minute sessions to train the objective of knee injury resistance. A brief period of that time is dedicated to strength work (bodyweight).
None of the plans known to us contain dedicated resistance training alongside neuromuscular retraining. Again, many contain bodyweight work. Few contain some medicine ball resistance training. But none contain heavy resistance work using barbells, kettlebells, dumbbells, and the like.
The common reasoning is that to improve strength without improving neuromuscular movements patterns only makes a bad movement and strong bad movement. Yet, this oversimplifies quality resistance training, in our opinion.
Neuromuscular training is not exclusive to plyometrics, jumps, and bodyweight movements. Quality movement can be taught using load, so long as it is appropriately progressed and scaled.
Our knee injury reduction training plan, called Athena, diverges from the common approach and combines neuromuscular training with resistance training. Progressions in the plan call for establishing good movement quality in unloaded, static conditions and progress to maintaining the trained movement quality into loaded and dynamic conditions. Simultaneously, the trained movement quality gained in unloaded conditions are separately progressed to add loading without increasing dynamism. In these two separate and simultaneous progressions, neuromuscular function is trained alongside strength.
The idea behind this is incredibly simple and yet somehow controversial: strong athletes have more control over their joints and the effects of external forces on those joints than do weak athletes. This is true since heavy resistance training increases the ability of the central nervous system to recruit more muscle. It also increases the quality of the contraction when recruited, both leading to better joint control. Also, properly coached strength movements increase movement quality. This translates to athletes using the proper muscles in the proper order and proportion during certain movements. After all, if adolescent girls are quad dominant, then coaches should make an explicit effort to train athletes’ hamstrings and gluteal muscles through squatting, lunging, and hinging. As athletes become stronger and better able to use these muscles then they can be trained with drills to use them in more dynamic situations. Or, they can be done alongside one another.
Plus, as girls develop, they don’t go through the same natural spike in testosterone that boys do and so they don’t develop the same amount of muscles as boys to mitigate injury risk. In other words, girls’ bodies outgrow their muscles’ ability to control these new body dimensions. It seems logical to conclude, then, that girls need to train to become stronger more than boys do, though this is far from the truth in athletic programs nationwide. In our experience and observation, there is more emphasis for girls on developing technical skill than acquiring strength. It is the opposite for boys, in a sense, where strength is gained first in order to be able to then acquire greater technical skill. Why is there a difference in athletic development approaches between the sexes?
Currently, we are conducting a study in coordination with Opedix, a performance clothing company, and the University of Denver to measure the effectiveness of Athena to reduce long term injury risk for adolescent girls. This is only the first of what will hopefully be a string of studies that move us closer and closer to finding an answer to reducing knee injuries endemic in young, developing female athletes. Yet, in this study, conducted by us, we are of course subject to – and therefore must avoid – confirmation bias. A bias where we look for data that confirm our own preconceived notions. In this case, we could selectively choose elements of data that suggest resistance training is the primary cause of knee injury reduction even though there may be not actual causal connection between the two.
In the current study, now having completed three weeks, certainly progress is being made. Interestingly, much of the initial stage of change for the girls was simply learning what it felt like for knees to dive and then what they could do to identify the cause of dive and finally apply the appropriate connection. Though they all have a solid understanding of the different things that can happen to put their knee at risk, they are still working to integrate the corrections and to consistently perform with initial success rather than applying a correction when they notice an error in their movement. These flaws are persistent but, at least in the short term, manifesting themselves to a lesser degree. Some of this may be simply that they are adapting to the specific work we are doing, and that when put into a different scenario, they will revert to old, bad habits. Only time will tell if the adaptations are program-specific or real. And only time will tell if the adaptations are permanent, semi-permanent, or simply short-term gains.