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Published on December 18, 2017

Include all muscle groups in your workoutInclude all muscle groups in your workout

All of the joints in our body are stabilized by static and dynamic structures.

The static structures are:

  • The intimate fit of the joint surfaces dictated by the shape of the underlying bone
  • The ligaments (i.e. the ACL in the knee attaching the femur and the tibia)

Dynamic stabilizers are the muscle-tendon units that cross the joint (i.e. the hamstrings and the quad tendons of the knee). Dynamic stabilizers can be changed by exercise or physical therapy, while static structures are constant unless degraded by trauma or corrected by surgery.

A joint functions best when the underlying bones are not deformed and the ligaments and tendons are well balanced. A muscle will function optimally when the central nervous system senses the muscle is opposed by an equally strong antagonist (i.e. the biceps and triceps oppose one another).

Sometimes muscles are coupled together and the strength of the two must be balanced for the joint to work properly. The shoulder is an example. While the large outer muscle (deltoid) lifts up the humerus, the rotator cuff keeps the ball centered in the shallow socket. When this imbalance persists the inevitable result is a progressively painful shoulder due to bursitis, tendonitis and eventual rotator cuff tear.

If there is no full thickness tear in the rotator cuff, physical therapy would be prescribed to address the strength mismatch between the rotator cuff and the deltoid. Once the cuff is strong enough to handle the forces generated by the deltoid, the symptoms typically resolve. The longer the imbalance persists the more likely surgery is necessary to repair or decompress the rotator cuff. Often I prescribe physical therapy, not for general weakness, but weakness of one muscle group relative to another.

Therefore, it is important when designing a workout program to include exercises for all muscle groups, not just the largest and most obvious ones.

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Timothy J. Kinkead, MD is an orthopaedic surgeon at Cape Cod Orthopaedics and Sports Medicine. He is a graduate of Yale University School of Medicine and completed his residency at Duke University Medical Center.