Fine motor control: An EMG study of ability of the thumb in healthy hands of adult subjects

Abstract

An EMG basic method of testing the fine motor control of the hand, a necessary clinical request, is needed to provide a practical approach on normal neuromuscular observations of the fine motor control parameters in order to interpret the harmonious motor functioning of the central and peripheral nervous systems. In this EMG study, predetermined voluntary writing movements were used to demonstrate various degrees of fine motor control (FMC) over the final common pathway in the abductor pollicis longus (APL) of healthy adult subjects. The effect of optimal motor control to isolate and maintain a single motor unit in the APL during motions of the thumb requiring different types of contractions, the speed of motions of the thumb, and the intensity of segmental muscular EMG activity of the first dorsal interosseus (1DI) and the opponens pollicis (OP) is researched. Observations led to the establishment of percentage levels of FMC achievements. The perfect FMC in the APL can be achieved in any of the tests given. However, each test has its own level of success and, therefore, its own degree of difficulty. The means of success of FMC of this group, being 80%, demonstrate the feasible degree of the testing procedure. Analyses of the means and of the frequency distribution of subjects related to levels of success of each static and dynamic test show increased FMC difficulty in fast continuous motions. Voluntary writing without assistance has a tendency to be faster in eccentric than in concentric contraction of the APL. The means of 1DI and OP stay at the light level of muscular intensity even in a fast upward writing motions, where these muscles should have primary or assistant roles. This illustrates the importance of testing the FMC in a highly coordinated task such as writing while dynamic elements of muscular contractions influence the motor control, and are affected by the FMC.