Contractile properties and fiber type compositions of flexors and extensors of elbow joint in cat: implications for motor control

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Abstract
Fiber type compositions and whole muscle contractile properties of selected muscles acting at the elbow joint in cat were investigated. Biceps brachii and brachialis, both flexors and anconeus and the 5 heads of the triceps brachii, extensors, were evaluated histochemically. Fiber type compositions of 3 superficial extensors, long, lateral and short triceps were primarily fast-twitch (FOG [fast-twitch-oxidative-glycolytic] + FG [fast-twitch-glycolytic] > 75%) as were both flexors. The deep intermediate and accessory portions of the medial triceps were about 87% type SO [slow-twitch-oxidative] and only anconeus was homogeneous with 100% SO fibers. Isometric contractile properties of most of these muscles were measured at the optimal length for maximal twitch tension. Mean values of contraction time and fatigue index for muscles composed mainly of SO and oxidative (SO + FOG) fibers were higher (78 ms and 0.87, respectively for anconeus) than for muscles with few SO and oxidative fibers (29 ms and 0.33 for lateral triceps). When stimulated at increasing frequencies, slow muscles increase tension output mainly between 5 and 15 pps [pulses per second] and fast muscles between 35 and 50 pps.