FIXATION MOVEMENTS
In all of the types of prehension described,
the hand assumes a fixed position. If the prehended
object is unyielding, reactions to the
flexion forces are afforded by the object. If the
object is fragile, or the hand empty, the hand
is maintained in any required prehensile
posture by cocontractions of the opposing
muscle groups.4
The characteristics of balanced muscular
action when supporting in the hand loads
which produce moments at the wrist have
been studied electromyographically by
Dempster and Finerty (6). In general, when
average potential amplitudes are used to
characterize the electrical activity of the
muscle, the curves of load-action potential
are linear. Frequencies range from 35 to 65
per sec. but bear no clear-cut relationship to
load. Typically, each of the muscles traversing
the wrist was found to function as agonist,
lateral stabilizer, or antagonist as the moment
load was shifted from direct opposition at