The muscular system can respond to trauma, repetitive overload, pathology or pain in a variety of ways. Muscles can become facilitated, overactive and even shortened in length, or they can become inhibited, weakened and atrophic. Individual muscles function in concert with entire groups of muscles throughout the body to maintain stability or produce movement. These individual muscles may be classified as agonists, synergists or antagonists. Clinically, we see the three following situations.
Muscle imbalance is probably the most common clinical presentation.
It occurs in a systematic fashion. Certain muscles which relate to the fetal position, static work postures or slumping have a tendency to become overactive or even shorten, while other muscles which relate to the neurodevelopment of upright posture or dynamic joint stability tend to become inhibited or even weak. Modern society's emphasis on constrained postures and sedentary lifestyles promotes an imbalance between overactive and inhibited muscles. The development of these predictable muscle imbalances is further spurred by the diminished afferent flow of sensory information from the periphery, in particular the sole of the foot, due to sedentarism and a lack of variety of movement. Naturally, movement patterns are altered and fatiguability increased, thus rendering the motor control system less able to adapt to various biomechanical sources of repetitive strain.