Mechanical properties of succinylcholine activated muscle fibers in the inferior oblique muscle of the cat.

To determine the mechanical properties of the multi-innervated fibres in inferior oblique muscle of the cat, these fibers were selectively activated by means of an intravenous injection of succinylcholine chloride (Sch). For small sinusoidal length changes (+/- 1 mm) of low frequency, tension in the Sch activated muscle exhibited a component that was sensitive to the direction of stretch but was independent of the velocity. At higher frequencies of length change (16 Hz) a form of negative friction was observed. Negative friction had not been previously noted in mammalian muscles, although a similar friction was observed both in the muscles of insects and amphibians. These properties were expressed in the form of a simple mechanical model.