The most common cause of back muscle pain is trauma, or injury. This may encompass several conditions, though the injury must occur through some sort of impact, strain, or other stress the body does not normally bear. Back muscle pain can also be caused by overuse of the muscle, muscle fatigue, muscle strains or ruptures, or even tightness due to weak muscles or tired muscles. Less often, back muscle pain can be caused by a herniated disc in the spine, or by nerve compression, particularly compression of the sciatic nerve that runs from the lower back all the way down the back of each leg.
Muscle strains are a common cause of back muscle pain. A muscle strain occurs when the tiny fibers that make up a muscle tear as a result of undue stress or twisting motions. The fibers usually repair themselves over time, and the RICE treatment — Rest, Ice, Compression, and Elevation — can be used for such an injury. The muscles will feel sore, tender, and even weak as a result of a muscle strain, and the injury will require several days of rest to allow healing to take place. More severe muscle strains may lead to a muscle rupture, in which the muscle tears completely from itself or its securing points. Such injuries are significantly more painful and usually require a surgery to repair the muscle tissue.
After physical activity, the muscles in the back can become fatigued, leading to back muscle pain. This is especially true if the person doing the physical activity is not used to such motions. The back muscles will become sore and tender, and they may feel tired for several hours or even days. This is not a severe condition, and rest and hydration along with some light stretching should solve the problem. If the pain lasts for several days, or if a muscle cramp occurs, the muscle fatigue may be part of a larger problem. Weak or underused muscles are likely to tire more easily, and when muscles tire, they tend to tighten. A tight muscle is more likely to become strained than a loose one, so muscle fatigue can ostensibly result in a muscle strain.
A herniated disc in the spine can lead to back muscle pain as well. A herniated disc occurs when the spinal disc, a capsule filled with a gel-like fluid situated between the vertebrae in the spine, ruptures and presses against the nerves that run near the spine. While this condition will not directly lead to muscle pain, the muscles of the back may tighten due to the extra strain placed on the back. The herniated disc often leads to sciatic nerve pain, which can cause changes in regular joint movement. This in turn can lead to muscle pain.