The neuromuscular system is responsible for all our interactions with
our environment. Although recent decades have witnessed numerous disco
veries that have shed light into various properties of this system, th
e basic principles underlying its overall operation still remain poorl
y understood. In this article, Carlo J. De Luca and Zeynep Erim discus
s the concept of common drive of motor units that Provides a possible
scheme for the control of motor units, unifying various seemingly isol
ated findings that have been reported. According to this concept, a po
ol of motor units that makes up a muscle is controlled collectively du
ring a contraction of that muscle. The unique firing patterns of indiv
idual motor units are effected, not by separate command signals sent t
o these units, but by one common drive to which motor units respond di
fferently. The specific architecture of the system and the orderly gra
dation in the inherent properties of individual elements enable a sing
le source to control the activities of all the motor units in a given
pool. Such an arrangement relieves the CNS from the burden of monitori
ng and regulating each motor unit separately.