ACL Tears in Young Athletes – How Can We Prevent This?

Every year several of our young athletes at Legacy Pediatrics experience a significant knee injury. A torn anterior cruciate ligament (ACL) can be devastating to the athlete both physically and emotionally. The numbers of ACL injuries in young athletes, especially in teenage girls, is skyrocketing and a great deal of research is underway both to better understand the problem and to find a solution. A new study may help unlock this problem: increasing strength in supporting muscles and changing the warm up routines of young athletes before practices and games could greatly lower the risk of these athletes experiencing an ACL injury.

How do these injuries occur? Most often an ACL tears when there is no contact with another player or the ground. The tear occurs when there is stress applied to the knee that the ligament can’t absorb. In a perfect world, the muscles of the leg absorb the energy that occurs when the body’s momentum slows or the body lowers to the ground. However, what the research shows is that the muscles are not strong enough to absorb the applied stress and the ligaments of the knee end up not being able to absorb the stress.

ACL Tears

The knee collapses inward creating excess stress on the ACL putting the athlete at risk of an ACL tear.

We can test for this muscle weakness by observing our athletes do a squat. A bowing inward at the knees instead of the leg remaining straight in line with the hips and feet during the squat is an indication of muscle weakness that has been implicated in ACL tears. What is the culprit? A relative weakness of some on the gluteal muscles, which keep the hip from internally rotating, is the problem. The outer gluteal muscle, the gluteus medius, abducts or moves the thigh outward. This movement prevents the thigh from moving inward, thus allowing the knees to stay in line and not collapse inward toward each other. Weakness of the gluteus medius muscle will put the knee in a position of stress on the ACL.

Another implicated cause of ACL tears is when the young athlete lands on a stiff or straight leg from a jump or a change of position. The ability to bend the knees and hips into a partial or deep squat position is dependent upon strong gluteus maximus, hamstrings and quadriceps muscles. Young athletes need to have enough strength in these muscles so that the muscles absorb the energy from the jump or position change and not the knee structures.

The best way to help young athletes reduce the risk of ACL injuries is to add strengthening exercises to build strength in the critical muscles; gluteus medius, gluteus maximus, hamstrings and quadriceps. This can be done easily and without any equipment by incorporating squats and walking lunges into the team’s training. Technique is critical! Inward collapse or caving in of the knees towards each other must not occur.

In addition to strengthening exercises, there is a very successful prevention program that provides neuromuscular training that can be substituted for any team’s warm up routine. The Prevent injury and Enhance Performance Program, PEP Program, consists of a warm-up, stretching, strengthening, plyometrics, and sports specific agility exercises to address potential deficits in the strength and coordination of the stabilizing muscles around the knee. A link to this program is provided below. We encourage families to discuss incorporating the PEP Program into their child’s team warm up routine with their child’s coaches. At the very least, the simple exercises can be performed at home before practices and games, and potentially prevent a devastating ACL injury.


A perfect squat technique has the knees behind the toes. The knees do not cave inward but remain in line with the hips and feet.

Squats strengthen the gluteal muscles, and when done properly with hips, back, and tibias vertical, they equally engage the hamstrings and quadriceps.


In a forward lunge, athletes step forward into a lunge and then return to standing, keeping the back straight and not allowing the knees to pass the toes. Lunges are also performed in the sagittal plane (not shown) to evenly strengthen the quadriceps, hamstrings, and gluteal muscles; improve core stability; and minimize strength imbalance between legs.


Side planks strengthen the abdominal and gluteal muscles. The athlete holds the position for 30 seconds, keeping her body in a straight line.

Resources for parents:

  1. Sportsmetrics
  2. PEP (Prevent injury, Enhance Performance)