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ACL Prevention Strategies Part II


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In the first part of this series, I discussed the ability to land properly on two feet to reduce stress on the knee and specifically the ACL. A safe landing requires sufficient ankle and hip mobility as well as hip and trunk stability. For any athlete that has to go overhead (basketball, volleyball, tennis, etc. ) landing places great demands on both thoracic spine and shoulder mobility and stability as well. Exercises were presented to address any limitations in joint motion, flexibility, or stability.

Now what happens when the athlete must land on one leg? Sport is unpredictable so training to land only on two legs can mean trouble down the road. Working on single leg strengthening is the first step and will be the topic of this article. Part III of ‘ACL Prevention Strategies’ will address training single leg plyometrics and landings.

Landing on one leg still requires a great deal of ankle and hip mobility as does landing on both feet, but the stability requirements are much greater. The muscles of the hip must work harder to absorb force during landing and to prevent the knee from going into an adducted and internally rotated position, also known as valgus (valgus = knees are moving inward and bending simultaneously = increased risk to tear the ACL). Trunk stability is also critical to ensuring good lower body alignment and maximum protection of the knee.

Training for the single leg landing must first begin with strengthening this pattern. You cannot land safely if strength is not first in place. This is where many coaches, trainers, and therapists make a mistake.

The single leg squat is the best exercise available to address lower body and trunk strength and stability with carry over to athletics and specifically single leg landings. The most basic form of the single leg squat involves the athlete sitting the hips back like he/she were going to sit down in a chair then standing back up. The trunk should be inclined forward and arms reaching forward to help counter balance the move. The non weight bearing leg is also kicking forward.

There are several ways to progress with this exercise, specifically to increase depth of the squat and maximize hip and trunk stability.

  1. Start with a target, such as a bench or chair. Sit all the way back and down to the surface in a controlled fashion. Lean forward and stand back up, still on one leg.
  2. Continue to use a target but now just lightly touch the surface rather than sitting all the way down.
  3. Progressively lower the height of the target until thigh is parallel to the floor. Some of my athletes will break parallel but must maintain knee control (this I will get to in a minute).
  4. Add weight by holding small dumbbells or a medicine ball in the outstretched hands. A weighted vest could also be worn to increase load.
  5. Change hand positions. Instead of always reaching straight out, take the arms right or left, even overhead but always work to maintain good knee alignment.

The key to the single leg squat is preventing the knee valgus angle. It is actually the job of the big hip muscles, specifically glute medius and maximus, to prevent the hip internal rotation and adduction that creates the knee valgus angle. Learning to keep the lower extremity stable with a slow, controlled movement like the single leg squat will go a long way toward preventing ACL injuries.

Joe Heiler PT, CSCS is a physical therapist specializing in sports medicine and orthopedics in Traverse City, Michigan. As a certified strength and conditioning specialist he has worked with athletes at all levels improving speed, power, and strength. Check out more great articles, exercise videos, audio interviews, and more from top physical therapists, athletic trainers, and sports performance coaches at


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