A muscle spasm is a sudden, uncontrolled contraction, or spasm that seems to happen without cause yet cause a great deal of pain. The muscle contraction and pain usually last for just a few minutes, and then slowly ease as the muscle gradually relaxes. While painful, they are harmless, and in most cases, not related to any underlying disorder. Still cramps and spasms can be manifestations of many neurological or muscular diseases.
The terms cramp and spasm can be somewhat general, and both terms are sometimes used to describe other types of abnormal muscle. These include stiffness at rest, slow muscle relaxation, and spontaneous contractions of a muscle at rest (fasciculation). Fasciculation is a type of painless muscle spasm, marked by rapid, uncoordinated contraction of many small muscle fibers.
Abnormal contraction of back muscles may be caused by an interruption in the central nervous system. For some reason, individuals temporarily lose heir ability to regulate muscle contraction and expansion.
Some researchers say that muscle spasms are caused by overly active motor neurons or overly sensitive muscle fibers that react without the usual stimulation that causes them to contract.