Innervation and "Tonus" of Striated Muscle in Man

Striated muscle is normally under a constant slight mechanical tension even when at rest and removed from the influence of gravity. This is shown by the fact that it contracts—to some extent even in the cadaver —when its tendon is severed. Also, contractures develop in otherwise healthy muscles after their antagonists have been out of function for a while. An increase of tension beyond what is seen at rest is noticeable in muscles or muscle groups serving to maintain posture, as in standing, without obvious movement. Resistance to passive movement, of varying degree in normal subjects and in patients suffering from a number of motor disorders, and stiffness of voluntary movement, experienced by patients suffering from spasticity and rigidity, illustrate possibly another form of tension in the muscle. All these various states of tension, obviously related in some fashion, and such unrelated states as turgor of tissues have been called