KINESIOLOGICAL ELECTROMYOGRAPHY - Biomechanics and Motor Control of Human Movement - page 250

10

KINESIOLOGICAL
ELECTROMYOGRAPHY

10.0 INTRODUCTION

The electrical signal associated with the contraction of a muscle is called
an electromyogram , or EMG. The study of EMGs, called electromyography ,
has revealed some basic information; however, much remains to be learned.
Voluntary muscular activity results in an EMG that increases in magnitude
with the tension. However, there are many variables that can influence the
signal at any given time: velocity of shortening or lengthening of the muscle,
rate of tension build-up, fatigue, and reflex activity. An understanding of
the electrophysiology and the technology of recording is essential to the
appreciation of the biomechanical relationships that follow.

10.1 ELECTROPHYSIOLOGY OF MUSCLE CONTRACTION

It is important to realize that muscle tissue conducts electrical potentials
somewhat similarly to the way axons transmit action potentials. The name
given to this special electrical signal generated in the muscle fibers as a result
of the recruitment of a motor unit is a motor unit action potential (m.u.a.p.).
Electrodes placed on the surface of a muscle or inside the muscle tissue
(indwelling electrodes) will record the algebraic sum of all m.u.a.p.'s being
transmitted along the muscle fibers at that point in time. Those motor units
far away from the electrode site will result in a smaller m.u.a.p. than those
of similar size near the electrode.