DEXTEROUS MANIPULATION CAPABILITIES ARE ASSOCIATED WITH CHANGE IN DISCHARGE RATE PROPERTIES OF MOTOR NEURONS WITH AGE

Abstract

Aging is accompanied by declines in manual dexterity and fine motor control. The purpose of this research was to compare hand motor control in young and older adults and examine the neuromuscular mechanisms responsible for enabling these interactions. We test force variability during isometric and dynamic contractions, manual dexterity and track motor unit activity to identify the neuromuscular mechanisms responsible for changes in dexterity with age. 26 older adults (66-86 years) and 28 young adults (19 – 38 years) participated in the study. Research participants performed force matching tasks during index finger abduction, precision pinch, static pressing and hybrid force/ motion tasks. The coefficient of variation (CV) during the force-matching task computed. Multichannel high-density EMG was measured from the First Dorsal Interosseus (FDI) and extensor Digitorum Communis (EDC). The EMG signals were decomposed to obtain motor unit discharge rate parameters such as discharge rate and discharge rate variability of the motor neurons was computed. Low-frequency common oscillatory drive to the motor neurons was computed using Principal Component Analysis (PCA) on the motor unit discharge rates. Associations between the force variability, dexterity scores and motor unit parameters were analyzed for group differences and associations. A higher CV of force was observed in older and younger adults was associated with reduced mean discharge rates, increased discharge rate variabilities and an increase in the low-frequency common oscillatory signal to the motor units. Additionally, the motor unit parameters were associated with performance on tests of manual dexterity such as the box and block test and grooved pegboard test.