MUSCLE MECHANICS - Biomechanics and Motor Control of Human Movement - page 224

MUSCLE MECHANICS

9.0 INTRODUCTION

The most intriguing and challenging area of study in biomechanics is prob-
ably the muscle itself. It is the “living” part of the system. The neural
control, metabolism, and biomechanical characteristics of muscle are sub-
jects of continuing research. The purpose of this chapter is to report the state
of knowledge with regard to the biophysical characteristics of individual
motor units, connective tissue, and the total muscle itself. The characteristics
of the individual units are described in detail, and it is shown how these
characteristics influence the biomechanical function of the overall muscle.

9.0.1 The Motor Unit
The smallest subunit that can be controlled is called a motor unit because
it is innervated separately by a motor axon. Neurologically the motor unit
consists of a synaptic junction in the ventral root of the spinal cord, a motor
axon, and a motor end plate in the muscle fibers. Under the control of the
motor unit are as few as three muscle fibers or as many as 2000, depending
on the fineness of the control required (Feinstein et al., 1955). Muscles of the
fingers, face, and eyes have a small number of shorter fibers in a motor unit,
while the large muscles of the leg have a large number of long fibers in their
motor units. A muscle fiber is about 100 μ m in diameter and consists of fibrils
about 1 μ m in diameter. Fibrils, in turn, consist of filaments about 100 ˚ Ain