Preventing ACL injuries in young female athletes
By Heidi Dawson

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The risk of ACL injuries in female, teenage athletes is up to six times higher than in male athletes of the same age, competing in the same sports. That's a pretty scary statistic for adolescent females, their families and coaches alike.

INDUSTRY PULSE

Do you teach neuromuscular training?
  • 1. Yes
  • 2. No

The consequences of such an injury can be huge — from a financial, physical and psychological standpoint — for both the short and long-term future of a young athlete. The average bill for surgery and pre- and post-operative care is estimated to be around the $20,000 mark. On top of the financial demand, research has shown that grades often drop, at least in the short-term and that girls are less likely to return to sports after such an injury.

Why are girls at a higher risk?

The risk of an ACL injury is highest in the 15-19 age group and among those playing sports such as soccer and basketball. The reason for this is the typical mechanism of the injury. The majority of ACL injuries occur when landing from a jump, performing a cutting maneuver to dodge an opponent or when decelerating suddenly. And it is this typical mechanism that holds the key to explaining why females are at greater risk of suffering this debilitating injury.

Video analysis has shown that during landing, cutting and decelerating movements on occasions when injury occurred, the knee tended to be in (or very close to) full extension; the body's center of mass was behind and away from the weight bearing limb and the knee was in a valgus position — i.e., with the hip internally rotated and adducted and the tibia externally rotated.

Biomechanical studies have identified four key neuromuscular problems that show how and why females adopt these positions when playing such sports.
  1. Girls often display an increased use of their quadriceps compared to their hamstrings, which results in increased knee extension on landing. This also increases the anterior translation of the tibia, pulling it forward and stressing the ACL.
  2. Girls tend to favor one leg more than the other. This results in an increase in strength on this side and asymmetric weight distribution when landing. This causes a shift in the body's center of mass, which as discussed above is a common position at the time of ACL tear.
  3. In general, girls have less core strength and stability than boys of the same age which limits their ability to correct shifts in their center of mass.
  4. Girls have a tendency to rely on their ligaments and tendons to reduce joint motion, instead of eccentrically contracting the muscles to slow and control their movement. This places higher stress on these structures and increases injury risk.


Prevention

As with all injuries, prevention is the best cure. A slew of recent research has centered around training programs as a way of reducing injury risk. The results of which indicate that a form of training termed neuromuscular training (NMT) can be highly successful in reducing ACL injury rates. In fact, pooled results from such studies have shown as much as a 72 percent reduction in these injuries amongst adolescent female athletes.

But what exactly is neuromuscular training? It's a phrase that has been used a lot lately, but very few athletic trainers, especially those coaching where it is needed the most — high schools — really understand what it is, let alone know how to introduce such a program.

What is neuromuscular training?

There have been many NMT protocols used when researching the effect of this type of training on ACL injury rates. A review of such research has concluded that the most effective programs contained three elements — core and lower limb strengthening, plyometrics, and feedback-driven technique modification.

Strength training should be targeted at muscle groups that can help avoid the typical ACL injury positioning. Strengthening the hamstrings helps to establish less knee extension and anterior tibial translation on landing, and strengthening the gluteal muscles will help reduce knee valgus by limiting hip adduction and internal rotation. Both of these muscle groups can be targeted using squat and lunge exercises, which also promote co-contraction of the quads and hamstrings — shown to be effective in decreasing the risk of most types of knee injury.

Strength training should also address the often diminished core strength of young females using exercises such as planks, swiss/bosu ball and balance board exercises.

Plyometrics include jumping and bounding exercises and should be incorporated into any NMT program. Start with simple double-legged take-off and landing exercises such as jumping squats and progress to single to double; double to single and then single to single take-off and landings. Initially such exercises should be performed for up to a maximum of 20 seconds at a time, provided form is good. This time can be gradually increased as strength and balance improve.

Feedback-driven technique modification is the area which is less well known when it comes to a recommended NMT program. Essentially what this means is teaching the athlete to recognize and avoid the valgus, extended knee position, which most frequently leads to these injuries. The coach is then constantly providing feedback to the athlete, encouraging, reminding and highlighting to them when such a position is adopted.

This starts with simple exercises such as squats where the athlete is not allowed to progress until they can consistently demonstrate correct knee positioning. Verbal cues are extremely useful here — reminding the athlete to land softly and stop the knee "falling inward."

So when and how should these programs be implemented? The most successful NMT research used a protocol that involved NMT training twice per week, with both sessions incorporating all three of the above components. A period of at least six weeks is required before neuromuscular improvements are seen. It is recommended that such training is continued during both the season and offseason and should start in the early teenage years to ensure the athlete is at the lowest possible risk when reaching the peak age group for such injuries.

Heidi Dawson is a graduate sports rehabilitator based in the United Kingdom. She runs two successful sports injury clinics and the injury website Rehab4Runners.