Abstract
Background:
Anterior cruciate ligament (ACL) rupture is a common injury that causes significant detriment to the athlete, including surgical cost, long recovery time, uncertain return to sport, and sequelae such as meniscus tears. Therefore, it is important to minimize the risk of sustaining an ACL injury. When adequately developed, trainable athletic attributes such as balance, proprioception, motor control, and strength can contribute to a reduction in injury.
Indications:
Athletic trainers or sports performance specialists may implement these exercises as part of a structured program during in-season or off-season training to reduce the risk of ACL injury in healthy athletes.
Technique Description:
The following exercises are categorized as training balance and proprioception or as training motor control and strength. The former category includes star squats on a balance board and 1-legged medicine ball tosses on a balance board. The latter category includes 1 hop to a 45° cut, weighted calf raises, and weighted single-leg squats.
Discussion/Conclusion:
Studies have found that engaging in a preventative program can significantly reduce the risk of sustaining an ACL injury. Athletes who did not partake in an ACL injury prevention program were nearly twice as likely to sustain an ACL rupture compared to those who did. Evidence suggests that neuromuscular training achieved specifically through incorporation of a balance board can contribute to injury prevention. Prevention of ACL injury is of paramount importance to athletes, coaches, athletic trainers, and physicians. Avoiding ACL injury can spare the athlete psychological distress, lost playing time, medical costs, and orthopaedic sequelae. Evidence suggests that a structured ACL prevention program can mitigate the risk of ACL injury. Furthermore, the exercises demonstrated are both time efficient and cost effective. It is important to note, however, that many factors contribute to ACL injury, including the athlete’s intrinsic biology and anatomy, the nature of their sport, and other confounding factors.
Patient Consent Disclosure Statement:
The author(s) attests that consent has been obtained from any patient(s) appearing in this publication. If the individual may be identifiable, the author(s) has included a statement of release or other written form of approval from the patient(s) with this submission for publication.
This is a visual representation of the abstract.
Video Transcript
In this video, we highlight neuromuscular training exercises that have been proven to help prevent anterior cruciate ligament (ACL) injury. We will review current literature on ACL injury prevention programs and then perform video demonstrations of key exercises.
We have no disclosures relevant to this presentation.
Background
In recent years, research has suggested an increase in adolescent ACL injury rates, likely driven by an increase in high school sport participation.1,2,11,17 We know that ACL injury also remains a challenge in collegiate athletics.3,8 To illustrate the scale of this problem, over 400,000 ACL reconstructions are performed each year in the United States alone. 5 These operations come at both financial and physiological cost. Yet, when athletes do not undergo ACL reconstruction, they are significantly more likely to sustain future meniscus injury.6,15 Given this background, there is a clear need to invest in efforts to prevent these devastating injuries with long-term consequences.
Indications
In a 2012 systematic review and meta-analysis of ACL injury prevention programs, Sadoghi et al 14 found that athletes who participated in injury prevention programs had a significantly lower risk of ACL rupture, with a pooled risk ratio of 0.38. Analyzing the studies featured in this analysis, as well as more contemporary work, we found that collegiate athletes and female athletes may derive the most benefit from these programs.7,9,10,12,18 Further, risk reduction programs using balance boards may be of greater efficacy.4,13,18
Technique Description
Given this research, we will demonstrate five exercises focused on both balance/proprioception and motor control/strength. These exercises will be demonstrated with collegiate athletes and feature the use of balance boards.
We will first explain and demonstrate 2 exercises focused on balance and proprioception.
For star squats, instruct the patient to begin by standing on 1 leg on a balance board. With their hands on their hips, ask the patient to bend their supporting leg while tapping the heel of their other leg on the floor in front of them. Instruct the patient to return to a standing 1-legged balance. Then, the patient will repeat this movement, this time tapping their heel to the side while bending their standing leg. The patient will come to standing and repeat this movement 1 more time, tapping their toes behind them. They have now completed 1 rep. Complete this exercise 12 times on each leg. While the patient is performing the exercises, instruct them to keep their gaze straight ahead and engage their core. Should the edges of the balance board hit the floor, encourage the patient to keep their standing foot in the center of the board, focusing on keeping all edges of the board off the floor.
The second balance and proprioception movement will require the patient to hold a medicine ball as they find their balance on a balance board. Once they find their balance on 2 legs holding the ball, ask them to lift 1 leg off the board and balance on 1 straight leg. Once they find their balance, instruct the patient to begin tossing the medicine ball to a wall or partner positioned in front of them. They will then catch the ball while maintaining balance on the single leg. One rep is complete once the patient has caught the ball and has regained balance on the board. Complete this exercise 10 times for 1 straight standing leg and then perform the same movement for 10 reps with the other standing leg.
After 10 reps have been conducted for each straight leg, instruct the patient to return to the leg they began the exercise with and to bend the knee of their standing leg. They should aim for about 45° of knee flexion. Have the patient lift the other leg off the board so they are balancing on just their bent leg. Again, instruct the patient to throw the ball against the wall in front of them and to catch the ball while maintaining balance on their bent leg. This is 1 rep. Have the patient complete 10 reps on each side.
The first motor control and strength movement that we will demonstrate is the forward hop to a 45° cut. To execute this movement, first instruct the athlete to stand on 1 leg. From this position, the athlete will jump forward, landing on the leg that performed the jump. Immediately upon landing, the athlete will make a 45° cut in the same direction as the leg that is being used to jump and land. For example, if the athlete jumped and landed on the right leg, then the cut will be directed to the right. Again, the athlete will land on the leg that performed the jump, this time sticking the landing. For visualization purposes, it can be useful to jump toward a line perpendicular to the direction of the original jump. This allows the athlete and clinician to best approximate the angle of the cutting movement.
This movement will be performed 10 times per leg, with all 10 reps being performed on the first leg before transitioning to the second leg. Between repetitions, simply instruct the athlete to walk back to the starting position. This exercise mainly focuses on the motor control domain. As such, it can be useful to the clinician to observe if there is inward movement of the knee in the frontal plane (valgus). This movement should be avoided and can direct the clinician to further improve strength and motor control during rehabilitation.
The second motor control and strength movement will be weighted calf raises. Direct the patient to pick up 2 dumbbells, holding one at each side, and stand with their feet hip-distance apart. Instruct the patient to slowly rise onto their toes simultaneously on both feet. Then they will raise 1 leg completely off the ground while staying on the toes of their other foot. Direct the patient to slowly roll through their standing foot, lowering back to the ground. Once the standing foot has returned to the ground, lower the other foot to stand in the starting position. This is 1 rep. Have the patient complete 10 reps lifting the same leg completely off the ground each time. Then, switch to lifting the other foot completely off the ground for 10 reps.
For a more advanced single-leg activity, instruct the patient to hold the dumbbells at their sides. Direct the patient to lift 1 foot off the ground. When the patient feels stable standing on 1 leg, instruct the patient to slowly lift onto their toes while squeezing their calf muscle. Once they have raised onto their toes as high as they can go, direct them to slowly lower back down to the ground. This is 1 rep. Complete 10 reps on 1 leg, and then direct the patient to perform the same movement with the other leg for 10 reps. The objective of this exercise can be modified to fall more in the motor control or strength domain. For strength gains, resistance should be increased progressively, whereas motor control can be advanced by introducing external stimuli or progression to performing this exercise on an unstable surface.
The final movement we will cover is the single-leg squat. To begin, instruct the athlete to hold dumbbells at their side. The athlete will then stand on 1 leg and raise their opposite leg off the floor. Instruct the athlete to perform a single-leg squat in this position by hinging at the hip, flexing at the knee, and dorsiflexing at the ankle. Appropriate depth for the squat may be dependent on the individual athlete; for example, an athlete's ability to dorsiflex at the ankle may limit the squat depth they can achieve before their heel lifts off the floor. The depth shown in the video is generally appropriate. Once proper depth is achieved, instruct the athlete to return to a fully upright position to complete the movement. Perform 12 reps on each leg, with all 12 reps being performed on the first leg before transitioning to the second.
To optimize the technique, it is useful to place a fixed object in front of the standing leg. Instruct the athlete to lightly touch the object with their knee while at the deepest point of the squat. Doing this promotes anterior translation of the knee while performing this movement. A foam roller is used in this demonstration as an example.
It is also important to avoid valgus alignment of the knee while performing this movement. Ensure that the knee tracks out over the toe during the entire course of the movement as opposed to drifting medially. Both proper and improper alignment are demonstrated here. This is another exercise that can have a principal goal of strength or motor control, depending on how it is advanced through time.
Discussion/Conclusion
These exercises pose no greater risk to an athlete than a typical fitness regimen, and there is a low cost associated with their implementation. Performing these exercises even has the potential to enhance athletic performance. 16 It is important to note, however, that many factors contribute to ACL injury, including the athlete's intrinsic biology, the nature of their sport, and other confounding factors.
As previously mentioned, athletes who do not partake in an ACL injury prevention program may be almost twice as likely to sustain an ACL rupture compared to those who do. 14 Research suggests that ACL injury risk reduction is particularly salient for collegiate athletes and for interventions using balance boards.4,10,12,13,18 Therefore, this demographic and the use of balance boards were featured in our selected exercises.
Prevention of ACL injury is of paramount importance to athletes, coaches, athletic trainers, and physicians. Avoiding ACL injury can spare the athlete psychological distress, lost playing time, medical costs, and orthopaedic sequelae. This concludes our video demonstrating key exercises used for ACL injury risk reduction. Thank you.
Footnotes
Submitted February 4, 2025; accepted April 17, 2025.
One or more of the authors has declared the following potential conflict of interest or source of funding: V.K.T. is a consultant with Smith & Nephew. AOSSM checks author disclosures against the Open Payments Database (OPD). AOSSM has not conducted an independent investigation on the OPD and disclaims any liability or responsibility relating thereto.
