In vivo iix and iib fiber recruitment in the gastrocnemius muscle
of the rat is compartment related.
Ruiter, C. J. De, P. E. M. H. Habets, A. De Haan, and A. J. Sargeant.
Institute for Fundamental and Clinical Human Movement Sciences,
Faculty of Human Movement Sciences, Vrije Universiteit, Amsterdam,
The Netherlands
APStracts 3:0111A, 1996.
The purpose of the present study was to investigate to what extent
fast twitch IIX and IIB fiber recruitment was related to the natural
existing muscle compartments (subvolumes of muscle innervated by
different primary nerve branches) in rat medial gastrocnemius (MG).
Three groups (n=6) of rats trotted on a motor driven treadmill (20
degrees incline) at different speeds. A fourth group served as
controls and a fifth group received in situ. electrical stimulation
of all MG muscle fibers. Post exercise glycogen levels (periodic
acid-Schiff (PAS) staining intensities) were made. Running caused
more, and in situ stimulation caused less glycogen breakdown in the
proximal IIX and IIB fibers compared to the fibers of the same type
in the most distal compartment. Furthermore, the boundaries of the
most distal compartment could often be recognized in the PAS stained
cross-sections. It was concluded that during running the proximal IIX
and IIB fibers were recruited to a greater extent (and at lower
treadmill speeds) compared to the distal IIX and IIB fibers
respectively.
Received 17 July 1995; accepted in final form 9 February 1996.
APS Manuscript Number A775-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 13 March 96