A reciprocal relationship exists between certain single muscles or groups of muscles, i.e., the tricep usually relaxes when the bicep contracts. An abnormal reciprocal relationship between muscles can cause a detrimental effect. When patients are examined for an obvious muscle spasm, for instance, utilizing bilateral muscle testing, it has been found that the majority of these patients have weakness in a muscle, rather than primary muscle spasm.
Muscles have the ability to adapt to their immediate environment.
Normal tonicity of muscular structures is illustrated below. It should be obvious to see how hypotonicity of one muscular structure would cause a contracture of the opposing or contralateral muscular structure. The body's balance would then become distorted. This can be seen in the person's body posture and orientation. The right arm and hand would be rotated with the palm facing either medially or posteriorly.