Nov 7th, 2013
Category: Injury Prevention
ACL Injuries within Young Athletes: Prevention & Training (part three)
Strength training has proven effective in reducing injuries in young and adolescent athletes. However, it was not and is still not always thought of in a positive light. Limited research and/or evidence have been available until recent times. The research and studies coming out highlight the importance of a progressive and age appropriate youth training program early on in athlete’s development years.
Coordination and neuromuscular inefficiencies result from alterations of the athlete’s center mass and bony lever system due to growth. Therefore, re-training all of the fundamental dynamic movements during times of growth is critical. It allows the athlete to learn and maintain proper movement patterns and efficient coordinative abilities.
Preparatory, mobility and non-impact sessions should be emphasized at the start of any program. Upon completion of the preparatory courses there should be a progressive model that increases load, volume, mobility, strength and motor skills that tax the neurological system. Age-appropriateness, gender differences and the athletic training age of the athlete(s) involved must all be taken into account.
Here are six focuses of a youth athletic training program:
1. Inability to efficiently activate the Gluteus Medius and Maximus (i.e. lack of strength)
As mentioned before in articles part one and two, knee valgus is a common trait in ACL injuries. The glute muscles, specifically the glute medius, controls the hip and lower extremity. The main action this muscle controls is adduction and femoral rotation. Both of these movements, if left unstable, result in high levels of shear force being placed on the ACL during dynamic movements. Strengthening the glute will decrease the likelihood of knee valgus and thus decrease the likelihood of injury.
Performing strength exercises focus on the glute, particularly in a unilateral fashion, can help develop the muscle while preventing muscular asymmetry (i.e. leg dominance).
® Single Leg Squat – perform this exercise by having them sit to an object such as a bench, chair, etc…
® Split Squats – ensure that their front leg knee doesn’t go beyond the front of the foot and that they push through their front legs foot / heel versus the ball of the foot.
® Side Planks – elicits favorable glute medius activation as well as rectus abdominis activation. This kills two birds with one stone.
® Single Leg Bridge – this exercise is difficult and should be worked up to. The athlete must be pushing off the heel and not the toes or ball of the foot.
2. Asymmetry of the lower extremities
Asymmetry refers to muscular strength / activity differences. These differences can be on two halves of the body and/or the same half. Leg dominance, which is a type of asymmetry, refers specifically to one leg being stronger than the other. Asymmetry can be solved by focusing on unilateral versus bilateral training, which should always be the focus of training early on. Example of this is performing unilateral split squats versus bilateral regular squats. Split squats allow for greater balance while reducing the flexibility requirement that can cause unfavorable movement patterns.
*Note: this model cannot be used for plyometrics (i.e. jump training). Unilateral plyometrics should always come after progressing through bilateral plyometrics.
3. Weakness of the posterior chain
Weakness of the glutes and hamstrings is major issue in young athletes. We previously addressed glute weakness, which now leads us to the hamstrings. Weakness of the hamstrings results in anterior dominance (i.e. quadriceps) over the posterior chain. When the anterior dominates dynamic movements overuse of the knee extensors and under activation of the knee flexors results. These high impact dynamic unilateral movements require high stress on the lower extremities. Overuse of the knee extensors during these movements are detrimental and will surely lead to an ACL injury (if not more).
Hamstrings also play a key role in resisting against lateral tibia rotation. Weakness of the hamstrings will not prevent this movement pattern from occurring and will thus result in excessive knee valgus. As mentioned before knee valgus is a major precursor for knee trauma.
Strength exercises for the hamstrings should place emphasis on the eccentric (i.e. downward) muscular action.
® Norwegian Hamstrings – emphasis is placed on core stability and eccentric muscular action
® Leg Curls – ensure that the athlete controls the stability ball or suspension straps when the feet are moving away from the glutes; maintain a high bridge position when the feet are near the butt
® Single Leg Romanian Deadlifts (RDL) – this is an advanced exercise that should be used and/or loaded with caution; proper knee flexion on the grounded side, an ability to maintain a flat back and properly utilizing the off leg as a lever to move the upper body towards the ground are all required
4. Core weakness thus leading to trunk dominance.
Although there is not a ton of research done specifically linking ACL injuries and core weakness together, it is worth noting that trunk displacement is a result of core weakness / stability; this results in altered dynamic knee stabilization. The less core stabilization athletes have the greater their body mass can be altered during dynamic movements.
Example isolated core strength exercises are:
® Side planks – activates the rectus abdominis, work stabilization and activate the glute medius
® Single Leg Bridges – focuses on core stability, lower back strength and glute strength
More advanced young athletes should be allowed to progress to more complex multi-joint movements such as Deadlifts, split squats and squat to press.
5. Re-training fundamental movements and/or learning fundamental movements.
The most critical training ages are 0-7 and 10-13. Why? 0-7 is when we learn our adult running gate and the majority of our dynamic movement patterns. Developing proper habits during this time, through simple repetition, is critical. Place emphasis on mobility, balance and movement mechanics. 10-13 is critical because these are the years when growth spurts begin to occur. The bony levers and center body mass are altered thus leading to altered dynamic movement patterns. The movements we learn from 0-7 can be lost during 10-13 if they are not practiced.
Focus your training on non-complex movement patterns that train proper running / sprinting mechanics and jumping / landing techniques. A study done a few years back found that athletes aged 9-11 improved their vertical jumping ability, as well as their overall balance, after a program that placed focus on fundamental core and lower body strength exercises (4).
*Note that at this age young athletes need a ton of verbal instruction, auditory cues and even more feedback.
6. Mobility issues in relation to growth spurts.
Mobility refers to an athlete’s ability to dynamically move through a range of motion (i.e. flexibility). In regards to ACL injury prevention, the quadriceps and hamstrings can be considered the most critical muscles. After all these muscles are responsible for knee flexion / extension and hip extension, which are required in dynamic movements. Maintaining flexibility throughout the entire body through self myofascial release therapy (foam rolling), contract/relax stretching and dynamic range of motion exercise is vital.
This article series was meant to raise awareness on a vastly increasing issue within our young athletic population. You can blame our lack of development on electronics, unsafe neighborhoods or anything else but that does nothing to solve the problem. Finding strength and conditioning centers near you with a coach who is fully aware of these athletic issues is critical to allow for proper youth development.
- 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: 765-773, 1996.
- 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.
- DiStefano LJ, Padua DA, Blackburn TJ, Garrett WE, Guskiewicz KM, and Marshall SW. Integrated injury prevention program improves balance and vertical jump height in children. Journal of Strength and Conditioning Research 24: 334-343, 2010.
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