Low Back Muscle Spasming – Introduction:
Similar to muscle spasming of the neck, low back muscle spasming is extremely common. After neck tightness, back tightness is likely the most common musculoskeletal complaint that a manual therapist will encounter.
The musculature of the back can be divided into the low back musculature of the lumbar spine and middle and upper back musculature of the thoracic spine. Being located posteriorly, back musculature functions concentrically to do extension of the trunk at the spinal joints. Back musculature on the right side can also right laterally flex and back musculature on the left side can also left laterally flex. The two largest muscle groups of the back are the erector spinae group and the transversospinalis group. Collectively, they can be grouped as the paraspinal group.
The psoas major and quadratus lumborum are two other important muscle of the low back. The psoas major is usually stated as a flexor of the lumbar spine, but depending on the lumbar spinal posture, it may also extend the lumbar spine (especially the upper lumbar spine). However, its most important function is likely stabilization of the lumbar spine, especially when motion at the hip joint is occurring. The quadratus lumborum is an extensor of the lumbar spine, but its most important functions are stabilization of the lumbar spine and elevation of the pelvis.
Muscle spasming is a term that describes increased active muscle tone when the muscle is at rest; in other words, increased sliding filament contraction. Muscle spasming can be global, in which case the entire muscle or a large portion of it is tight; or it can involve myofascial trigger points and taut fibers.
Low Back Muscle Spasming:
Low back muscle spasming is common because paraspinal extensor muscles of the lumbar spine must contract to support the weight of the entire body above (trunk, neck, head, and upper extremities) whenever we bend down in front (into flexion). As we bend down, they eccentrically contract to slow our descent into flexion; and as we return to an upright position, they must concentrically contract to extend the spine. And if we remain bent over in a partially flexed position such that the center of weight, in other words the center of gravity, of our trunk/upper body is not balanced over our pelvis, then the lumbar paraspinal muscles must isometrically contract to maintain this imbalanced position. If an object is being picked up or held, it requires that much more contraction force on the part of the lumbar paraspinals, especially if the object is heavy or if the object is being held far from the body. In effect, extensor muscles of the low back must constantly work against gravity (and do so with poor leverage force compared to the force of gravity on our trunk’s center of gravity).
Because we so often bend and work down in front of ourselves, the low back paraspinal musculature is often overused and tightens as a result. This is true regardless of whether we are stoop or squat bending. Stoop bending is worse because the spinal facet joints are in flexion, which is an unstable open-packed position requiring greater muscle contraction force to stabilize them. However, even if we squat bend and keep our spinal joints in a stable closed-packed position of extension, if the center of gravity of the trunk is imbalanced anterior to the pelvis, the lumbar paraspinal musculature must work to keep the trunk from falling forward into flexion. Only if we bend from the hips, knees, and ankles and keep our back vertical, and therefore the center of gravity of the trunk over the pelvis, will the musculature be spared from having to work so hard.
Lumbar paraspinal musculature also often tightens as a part of lower crossed syndrome. In this syndrome, the pelvis has an excessive anterior tilt and the lumbar spine has an excessive lordotic curve (of extension). This causes a shortening of the lumbar paraspinals and by the principle of adaptive shortening, they increase their tone and become tight (locked short). Because the psoas major is an anterior tilter of the pelvis, it also often tightens as a part of lower crossed syndrome.
Another common reason for low back musculature to tighten and spasm is as a protective mechanism for an underlying pathologic condition of the lumbosacral spine. Examples include a pathologic disc, joint hypomobility dysfunction, facet syndrome, a lumbar strain or sprain, or a condition of the sacroiliac joint. Therefore, any factor that tends to cause or aggravate any of these conditions will likely result in tightness and spasming of the low back.
Middle/Upper Back (Thoracic Region):
Tightness and spasming of the paraspinals and other musculature of the middle and upper back (thoracic region) is not as common as low back muscle spasming, but does often occur. Tightness in this area can be caused by many factors. Just as bending the trunk forward can tighten the low back paraspinals, bending the upper trunk and neck forward can similarly tighten the thoracic paraspinal muscles. Therefore, thoracic paraspinal tightness is often linked to conditions of the neck. And just as lumbar tightness occurs as a part of lower crossed syndrome, thoracic tightness often occurs as a part of upper crossed syndrome. In upper crossed syndrome, the upper back becomes rounded into flexion, in other words, the thoracic spine’s curve becomes hyperkyphotic. This causes the thoracic paraspinal musculature to become tight (locked long). Many postures and activities can cause or exacerbate upper crossed syndrome. Examples include working at a computer and riding a bicycle. Upper crossed syndrome also involves protraction of the shoulder girdles and medial rotation of the arms at the glenohumeral joints. This places further stress on the thoracic region, often resulting in tightness of the shoulder girdle muscles in the thoracic region (middle trapezius and rhomboids).