Neuromuscular effects of stress

Introduction
One of the effects of stress is a general increase in tension within the skeletal muscles. This muscular tension occurs generally, but affects some areas more than others.

The muscles which are typically affected by stress include the shoulder elevators, the muscles of the neck and jaw, the accessory muscles of breathing and the diaphragm. The erector spinae are a commonly affected muscle group. Muscles which are already under tension due to postural distortions or for other reasons may develop problems secondary to the increased muscular tension. Muscles which are used repetitively during the period of stress are often held with more tension in them than is necessary (e.g muscles of the shoulder and arm when typing), and if this behaviour occurs often the tension may become habitual.

Neuromuscular hypertension
When stress remains at fairly high levels over a period of time neuromuscular hypertension can develop (Hertling & Kessler, 1996).

The nervous system becomes accustomed to a certain level of tension in the muscles and begins to habitually and unconsciously hold this tension in the muscles (Hanna, 1988). If stress continues to impact the individual, this muscular tension can become sustained at higher and higher levels (Hertling & Kessler, 1996).

Chronic muscle tension has a number of negative impacts on the body


 * Local Adaptation Syndrome – the local tissues experience ischemia, and adapt accordingly
 * Trigger point formation occurs after a period leading to pain
 * Hypertension – isometric exercise has been shown to increase blood pressure dramatically. When muscles are chronically tight, agonists and antagonists are locked in a continuous isometric contraction. The natural result of this is hypertension (Hanna, 1988).

Stress and Pain
Because stress tends to increase muscle tension, it also tends to increase pain. The severity and duration of many musculo-skeletal conditions are increased with stress (Hertling & Kessler, 1996).

If someone is recovering from an injury, or some type of painful condition it's important to keep their stress level in check. This is because the sustained neuro-muscular tension associated with chronic stress can create an environment conducive to trigger point development and activation (McQuillan, 2008). Trigger points can remain in the body long after the original condition has subsided, and are frequently a significant factor in chronic pain.

Neuromuscular Stress Reflexes
Thomas Hanna, founder of the Somatics method of treatment described three neuromuscular stress reflexes which are useful in understanding the muscular effects of stress on the body, and the development of postural distortions.

The landau reaction activates the extensor muscles of the body and is also called the extensor reflex. This reflex is associated with assertive engagement with the world.

The startle reflex activates the flexor muscles of the body, and is also called the withdrawal reflex or the flexor reflex (Schleip, 1993). This reflex is associated with withdrawal, and emotional collapse.

According to Hanna, chronic activation of these two reflexes is the primary cause of biltareal postural distortions (ocurring in the mid-sagittal plane - e.g. head forward, pelvic tilt). Hanna sees the trauma reflex as the primary cause of unilateral postural distortions (occuring in the frontal plane – e.g. one hip/shoulder higher than the other) (Hanna, 1988)

Here's a link to an article which explains these three reflexes.

An expanded view of the three reflexes of stress, Lawrence Gold.