The rate of tension development in isometric tetanic contractions of mammalian fast and slow skeletal muscle

Following the demonstration by Buller, Eccles & Eccles (1960b) that the speed of contraction of mammalian skeletal muscles was at least partially determined by the motor nerve innervation, two central problems remained. First, what part or parts of the contractile machinery of the muscle are influenced by the motor innervation, and, secondly, how do the motoneurones bring about their influence upon the muscle fibres? The solution of the first of these two questions requires a more detailed study of the contractile mechanism of mammalian muscle than has hitherto been made, with particular attention to any differences which exist between fast and slow skeletal muscle. In the mammal, both the fast and slow skeletal muscles consist of twitch fibres, and both types of muscle are therefore comparable with the fast fibre system of the frog. Only very recently has there been a demonstration of the equivalent of the frog slow fibre system in mammalian muscles, and as yet such fibres have only been identified in extrinsic ocular muscles (Hess & Pilar, 1963). The present paper is concerned with an investigation into the rate of isometric tension development in mammalian fast and slow muscles following repetitive stimulation of their motor nerves. This study was a necessary preliminary to the understanding of the alterations which occur in the rate of tension development following operative cross union of the nerves to mammalian fast and slow muscle (Buller & Lewis, 1964, 1965b). A preliminary account of some of the experiments herein reported has already been published (Buller & Lewis, 1963 a).