Electromagnetic method for in situ stretch of individual muscles.

A technique for stretching individual muscles in intact behaving animals via chronic intramuscular implantation of a permeable slug and use of an external electromagnet to apply force to the slug has been developed for use in the study of the role of sensory input due to muscle stretch in the control of skilled motor activity. This paper is an analysis of the force exerted on a permeable slug by a solenoid, and a discussion of practical aspects of design and control. The force exerted on a slug inside a coil is a function of slug length, cross-sectional area, and magnetisation properties and of coil size, geometry, and current. The force inside the coil may be increased by surrounding the coil with a permeable sleeve and thereby increasing the field strength inside the coil.