ACL Injuries within Young Athletes: Precursors (part one)

Nov 7th, 2013

Category: Blog

ACL Injuries within Young Athletes: Precursors (part one)

ACL Injuries within Young Athletes: Precursors (part I)

Founder of Functional Muscle Fitness

Year round participation in sports seems to be on the rise in the youth population; not coincidently, so is the injury rate. Limited range of motion (ROM), muscular weakness, inactivity and various other traits, which are a result of limited physical activity outside of sports, have lead to an increased population of underdeveloped youth. More specifically, underdevelopment within the posterior chain and core is a leading cause of injury.

ACL injuries amongst young athletes are on the rise. Athletes between the ages of 10 and 13 are moving through movement patterns that are associated with major ACL trauma (1). Children even younger are showing high risk movement patterns during dynamic athletic movements such as jumping, sprinting, running, cutting and stopping. Some of these high-risk movement patterns, particularly within the lower extremities, are knee valgus, reduced knee flexion and excessive lower limb rotation. Each of these movements can be assessed during squatting and/or during athletic movements.

Knee valgus, which is a precursor to non-contact ACL tears, is when the knee collapses inward during times of knee flexion (i.e. single leg squat). Knee valgus is a result of weakened posterior chain. This can lead to over extending during dynamic movements that limits the activation of the stretch shortening cycle required in athletic movements. The stretch shortening cycle (SSC) is the utilization of the muscles, tendons and ligaments in a spring like manner. If the knee is overextended then the athlete limits their performance while increasing their risk of ACL trauma.

Leg rotation, along with knee valgus, is another precursor to ACL trauma. Leg rotation indicates that the athlete has an inability to control his or her lower extremities due to underdevelopment of the posterior chain.

Insufficient strength, underdeveloped fundamental skills and rapid or even steady growth are all leading causes of ACL injuries. Developing fundamental athletic skills in a safe and progressive manner is appropriate for increasing sport skill and preventing injuries. A common mistake most coaches/athletes/parents make in youth training is placing emphasis on specialization training versus fundamental athletic motor skills. Rather than focusing on a specific sport coaches should place emphasis on mobility, flexibility, symmetry, strength and do so by progressively increasing load, volume and biomechanical complexity.

Rapid progression in reference to youth athletic training is incorrect. No coach should attempt to teach young athletes complex multi-joint movements and/or exercises until they have had ample time to master fundamentals. In fact, it is blatantly contraindicated by nearly all scientific research (1, 2). Young athletes are generally unable to master complex motor skills until around the ages of 10-13. Other factors must be accounted for such as their training age and the type of training they have been previously engaged in. Adopt a “less is more” approach to youth training; simple repetition is gold when it comes to youth development.

A commonality in youth sports today is overuse injuries, particularly those participating in year round sports. Much of these injuries could be avoided if more emphasis was placed on the fundamentals of athletic movement, mobility, muscular symmetry and overall fitness.

During times of major growth spurts strength and conditioning coaches and/or personal trainers must account for reduced coordination abilities. The growth plates are wide open and are susceptible to fracture, which is a major reason age appropriate fundamental movement patterns must emphasized. More specifically, core strength, coordination and proprioception (i.e. ability to balance while unbalanced) training will drastically enhance their neuromuscular abilities while increasing flexibility. Therefore, developing fundamental athletic movements during this period in their life, which is often call “awkward adolescence,” is critical.

Continue reading onto part two of ACL Injuries within Young Athletes… Gender Differences to learn about the differences between the genders as it relates to athletic performance and ACL injuries.



  1. Hewett, TE, Stroupe AL, Nance TA, and Noyes FR. Plyometric training in female athletes: Decreased impact forces and increase hamstring torques. Am J Sports Med 24: 765-770, 1996.
  2. Henja WF, Rosenberg A, Buturusis DJ, and Krieger A. The prevention of sports injuries in high school students through strength training. National Strength Conditioning Association Journal 4: 28-30, 1982.


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