The most common use of the term refers to a loss of muscle volume which occurs due to a reduction in the size and/or number of muscle fibers. The most common causes include atrophy secondary to disuse of the muscle, compromise of nerve fibers which go to (innervate) the muscle, or due to a disease process within the muscle. Muscle atrophy is associated with a loss of muscle performance and strength. Weakness associated with mild atrophy may be obvious and may only manifest as exertion induced weakness (muscle fatique). Spinal nerve damage can result in muscel atrophy of select muscles of the torso or extremities.  Chronic back pain can lead to disuse and atrophy of deep spinal muscles. This can further result in abnormal spinal segment movement.