ACL Series: Risk Factors

Over the past few years much of the research, including a recent review (Bien, 2011) named the several biomechanical/neuromuscular risk factors for non-contact ACL injury, as well as the most effective programming implementations for prevention. Here are the area’s we focus on in our program model:

  • Hip and Knee Pathomechanics
  • Hamstring Activation and Strength Deficits
  • Leg Dominance & Balance Factors
  • Core Strength and Propreoceptive Factors
  • Agility and Plyometric Training
  • Program Duration and Adherence

Over the last 10 years, our program has evolved from one that simply uses warm ups designed to reduce the risk of injury, into a sports performance program that addresses each of the factors above within every facet training. We made this change when we realized that simply warming up with a few key exercises did not fully prepare our players for the high speed, reactive environments in which they compete. A more complex and comprehensive model was needed, and now after training in this environment for sometime, we are seeing a level of performance that has exceeded our expectations while still maintaining our focus on reducing the risk of injury.

We start off looking at the hip and knee joints and the way athletes get in and out of jumping, landing and change of direction (pivoting) movements. The research states that athletes participating in aggressive, pivot based sports such as soccer, football, basketball, etc. have a high risk of injury to the knee.  To understand this we need to look at what factors/mechanics may be present that might elevate the risk of injury in these athletes.

What the research says:

  • Knee valgus angles and moments seem to be primary predictors of ACL injury risk in female athletes.
  • Positioning of the knee and hip may be very crucial in preventing ACL tears as more injuries seem to occur when the athlete lands or plants to change direction without ample hip and knee flexion.
  • Fatigue seems to elevate risk as knee valgus and hip rotation seems to be more pronounced as the athlete fatigues.
  • Athletes that are Efficient Anticipators of landings and change of direction situations position themselves more efficiently, and have show to have a decreased risk of injury when compared to those who are slower to recognize or react to chaotic environments.

In summary, as fatigue sets in, athletes who fail to anticipate and properly position their body to control these quick, transition based changes of direction, may put themselves into situations that result in excessive knee valgus or hip rotation, and therefore put themselves at risk of a serious knee injury.


The second biomechanical/neuromuscular risk factor in our list targets the hamstring, and looks primarily at the balance or symmetry between the hamstring and quadriceps muscles of the upper leg. According to the research, failure to efficiently recruit the hamstrings as the player decelerates (landing after a jump or decelerating to change direction) may cause a decrease in knee “stability” as it moves forward or rotates laterally. Especially in young females, who have been shown to have a lower strength to body weight ratio when compared to their male counterparts, training to use the hamstrings to control the knee positioning becomes increasingly important.

The third factor in regards to reducing the risk of lower extremity injury involves balance and leg dominance. Almost every athlete will have a dominant leg, and interestingly enough, with sports like soccer and basketball it is often the left leg (plant leg in soccer or take off leg in basketball lay up drills) in right handed/footed athletes that is the dominant leg in regards to strength, power and balance.

This makes perfect sense when you see the number of repetitions of dynamic jumping or deceleration to plant before kicking or jumping, that the athlete will perform in a given workout. Focusing on isolation, as well as integrated movement, is a key factor in reducing the risk of injury, as it will develop an athletic balance between legs as well as muscle groups within each leg. Single legged activities should be instructed from a balance and isolation perspective in the beginning of the program, then progress to more dynamic jumping/hopping and landing exercises and finally, a more plyometric or power development approach is utilized.

The fourth factor stated in the research involves torso control and propreoceptive repositioning. If we direct our attention away from the knee and up to the torso, we often notice that, in moments of injury, there is a combined effect of valgus knee motion and torso sway (or lateral trunk flexion). This creates the perfect storm for a potential ACL tear by creating extreme forces at the knee, while the athletes have put themselves into positions where they cannot effectively stabilize or control these forces acting on the knee.

The fifth factor in our overview of the research on reducing the risk of lower extremity injuries involves what is commonly known as the feedforward mechanism or anticipation of responsive action. This section is all about the athlete being ready, or positioned in such a way, as to prepare for deceleration and subsequent reaction to a situation or other player’s movement.

What the Research Says:

  • ACL injuries occur in less than 100 milliseconds whereas reflexive activation takes an estimated 128 milliseconds. This suggests that ACL injuries occur too fast to allow a reflexive muscular response to prevent the injury.
  • Successful prevention programs use the feedforward mechanism for dynamic lower extremity stability.
  • Pre-activation may increase knee joint stiffness and dynamic stability to protect articular structures.

This mindset of decreasing joint stiffness goes against the goals of most plyometric programs that try to increase joint stiffness to get a quick stretch shortening cycle type response. This may be why you will typically find physical therapy programs or injury prevention programs emphasize “soft” landings or “quiet” landings in jumping activities.

While this makes sense from a reduction of risk standpoint, it is not preparing players to be explosive on the field or court. For instance, how many times have you seen a player land after rebounding a basketball with a slow absorption or deep, soft or quiet landing to a parallel squat position? This just doesn’t happen in sport. The key here is to get the player to initiate the deceleration as they land (feedforward mechanism), and quickly get into an athletic position that still allows them to be “plyometric” (or springy with efficient joint stiffness) while also having enough knee and hip flexion (bend) to be safe.

Creating an Exercise List:

As we looked at the factors that may reduce the risk of injury, we also looked at the research suggested exercises for both reduction of risk as well as rehabilitation.  Here is a list of the top 15, research suggested exercises, and our favorite progressions broken down by category:


  1. Marching and Bracing
  2. Rollout Exercises
  3. Plank Positioned Rotation, Flexion, Extension
  4. Side Plank with Adduction
  5. Glute Bridge

Hip and Knee:

  1. Dynamic Balance and Rhythmic Movement
  2. Single Legged Leg Press, Leg Extensions, Leg Curls
  3. Single Legged Deadlift or 1L RDL with Rotation
  4. Step Up, Lunge and Split Squat

Jumping and Landing:

  1. Box Jump to Stuck Landings, Rhythmic Hops
  2. TRX 1 Leg Squat, Box Step Up, Step Up Jumps, Lateral Stair Work
  3. Single Legged Jump (Hops), Squats & Jumps with Dumbbells


  1. Elastic Plyometric Training


  1. Planned and Anticipation Based Agility
  2. Reactive Agility Training

This post is a paraphrased version of our complete ACL Return to Confidence Program manual. If you would like to request a copy of this manual which lays out the specifics of each of the 5 categories in much more detail, please contact me at