When people think about muscles, they think about strength. However, muscles have two jobs: to contract and to relax. Muscle contraction causes the muscle fibers to shorten in length, pulling the attached bones with it. This muscle action is the bases of all skeletal movement. If the muscle does not relax after contraction, it is considered hypertonic, spastic or over-active. Hypertonicity causes the skeleton to get stuck in all sorts of abnormal positions and postures. And hypertonicity leads to joint pain. In combination with muscle weakness, hypertonicity amounts to poorly functioning muscles. Muscle therapy is meant address such weakness and hypertonicity in order to create better muscle function and improve painful conditions like shoulder tendonitis, neck pain, and back pain.
Many types of muscle therapy do a great job improving strength, but neglect the relaxation component of muscle function. On the other hand, there are a handful of muscle therapies which induce the relaxation of hypertonic muscles and restore balance between a muscle's two jobs: contract and relax. One such technique is called Muscle Energy Technique (MET) which is similar to proprioception neuromuscular facilitation (PNF) and facilitated stretching. Muscle energy techniques take advantage of natural physiologic responses between agonist-antagonist muscle groups. For example, when the elbow is bent as the bicep muscle contracts, the antagonist muscle to the biceps, the triceps, relaxes. This response is called the reciprocal inhibition. Another example of a natural physiologic response is called the post-contraction inhibition. After a muscle contracts, there is a finite "latent period" in which time a second contraction is inhibited.
Taking advantage of this post-contraction inhibition is most important for inducing relaxation in a hypertonic muscle and is widely utilized in MET.
Of course, there are variations in muscle energy therapy based on the degree of contraction and the amount of stretching. But, the same primary goal applies: to restore balance between agonist-antagonist muscle groups. This balance helps maintain proper joint position and joint load. A muscle researcher wrote:
The mixture of tightness and weakness seen in the muscle imbalance process alters body segment alignment and changes the equilibrium point of a joint. Normally, the equal resting tone of the agonist and antagonist muscles allows the joint to take up a balanced position where the joint surfaces are evenly loaded and the inert tissues of the joint are not excessively stressed. However, if the muscles on one side of a joint are tight and the opposing muscles relax, the joint will be pulled out of alignment towards the tight muscles.
A common example of pain caused by abnormal muscle balance is neck pain. The neck is constantly pulled out of alignment because the anterior neck flexors become weak while the posterior neck extensors become too strong. This imbalance between an agonist-antagonist muscle group leads to abnormally increased lordosis (arch) of the neck. With increased lordosis, sensitive structures in the neck become stressed and painful like ligaments, joints, and nerves. This example of neck pain represents a perfect opportunity for muscle therapy.
The effectiveness of muscle therapy can be variable depending of the quality of the muscle isolation, the joint integrity, and the tolerance of the therapy. Every therapist and every patient is different. But when pain is unrelenting, muscle therapy is worth a try. Those who do not have pain should also take notice because the balance of tight muscle versus weak muscle is important for any fitness program. Disregard for muscle function in its entirety can lead to a chronic painful condition. Tight muscles need to relax before weak muscles can be strengthened. Remembering that fact and remembering that muscles have two jobs, to relax and to contract, can result in better exercise outcomes.