Transformation of morphological, functional and metabolic properties of fast-twitch muscle as induced by long-term electrical stimulation.

Transformation of structural, functional, metabolic and molecular characteristics is induced by stimulating fast-twitch muscles with the frequency pattern of a motoneuron normally innervating a slow-twitch muscle. These changes correspond to a transition of a "fast-white" into a "slow-red" muscle. Intermittent stimulation (8 h/d) does not affect the system but causes alterations of the sarcoplasmic reticulum which lead to changes in time to peak and half relaxation time. Continuous stimulation (24 h/d) induces a transformation of the muscle also at the level of the myosin system.