Muscle Imbalance and Common Overuse Injuries

By Robert Donatelli, PhD, PT

An overuse injury in sports is very common. Pain in the front of the knee, patellofemoral pain syndrome, patella tendon strain, hamstring strain, hip strain and rotator cuff strain are conditions I treat on regular bases in my population of athletes. An overuse injury is difficult to diagnosis because of their gradual onset and intermittent pain. The most common cause of an overuse injury in athletes is muscle dysfunction.

Muscle is the best force attenuator in the body. They initiate movements, slows down movements, and control movements of bones. In other words muscles are our best shock absorbers. Our joints are surrounded by muscle to accomplish the above functions. In order to accomplish the functions described above muscles must work in groups referred to as agonist and antagonist. One muscle group initiates movement and the other muscle group controls movement.

If some muscles fatigue because of prolonged activities such as tennis, the muscle is no longer an effective shock absorber. As a result of fatigue the muscle can become damaged, resulting in weakness, poor flexibility, and inadequate endurance. Muscle imbalance results from weakness, poor flexibility and inadequate endurance in either the agonist or the antagonist. For example, Elliot B and Achland, (Biomechanical effects of fatigue on 10,000 meter running techniques. Research Quarterly Exercise and Sports 52:160-165, 1981), used high- speed cinematography to study the effect of fatigue on the mechanical characteristics in highly skilled long distance runners. They found that, toward the end of the race, the runners exhibited less efficient positioning of the foot at foot strike as well as decreased stride length and stride rate. All of which is placing the runner at risk of developing an injury.

The knee is very susceptible to an overuse injury because of muscle imbalance. Weakness of the hamstring muscle group can cause increase strain to the anterior cruciate ligament (ACL). Hamstring muscle tightness in the presence of quadriceps femoris muscle (front thigh muscle) weakness has been associated with anterior knee pain. The tightness of the hamstrings increases the compressive forces to the patella femoral joint (Knee Cap). Quadriceps femoris muscle weakness, especially in the vastus medialis, (the inside of the thigh muscle group); can result in lateral patella tracking during knee flexion and extension. The patella (knee cap) should follow a grove on the end of the long bone of the thigh (femur). Muscle imbalance can change the patella’s ability to track effectively.

In addition to the muscle imbalance between the quadriceps and hamstring muscle groups, muscle imbalances with the hip can also cause patella femoral tracking problems. We have observed that weakness of several key hip stabilizers such as the hip abductors (on the side of the hip) and hip external rotators (muscle that move the foot toward the opposite leg) have a devastating effect on the patella-femoral joint. A recent study demonstrated a significant correlation between weakness of the above hip muscles and injury to the lower leg in athletes. (Leetun, Lloyd-Ireland et al. Core stability measures as risk factors for lower extremity in athletes. Vol 36: 926-934, 2004). The athlete must possess sufficient strength in hip and trunk muscles that provide stability in all planes of motion.

Prevention of Muscle Imbalace and Overuse Injuries

Strength training is the best prevent of muscle imbalance and overuse injuries. We incorporate the use of free weights and machine weights in our hip and trunk exercises. Rotational exercises are not commonly seen in the gyms of America. However, strengthening the hip rotators is very important to the athlete.

Also, try the hip rotation exercises shown. Lie face down on a pillow and move the ankle to the left and right. Go all the way to the end of the range of motion by trying to move your foot toward the floor. You may want to use an ankle weight with the exercise to make it more difficult.

Your hip is your center of gravity, and a weak hip can have disastrous effects—particularly on your lower limbs because the hip is where all motion in the lower leg starts. Hip muscles and ligaments are among the strongest in the body and they can affect gait, quickness, agility, and explosive power.

For athletes, balancing the hip muscles can be the difference between winning versus losing and between an injury-free season versus disabling muscle strains. I have observed numerous cases in which pain and muscle dysfunction were caused by major deficits in the hip muscles. I also have seen significant changes in athletes’ performances as a result of strengthening their hip muscles.

By keeping your muscles strong, you will prevent an overuse injury. You know the proverb: “An ounce of prevention is worth a pound of cure.”

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