Abstract

The measurement and assessment of maximal voluntary rate (MVR) are essential to our understanding of the limiting factors associated with motor control of human movement. However, very little is known about the dynamic changes that occur throughout an MVR task and how these changes impact upon normal functional capacity, especially with respect to aging and selected clinical populations. The purpose of this study is to test the functional capacity of the motor system and to compare any age-related changes in kinematics and electromyographic (EMG) parameters between young and older groups. Using a simple but novel MVR task (e.g., flexion and extension of the index finger for 20 s) developed by Rodrigues and colleagues (2009), we collected data on both the dominant (right) and non-dominant index fingers. With respect to the dominant finger, both groups experienced an immediate and continuous decline in peak movement frequency and velocity of the flexor and extensor. Significant group differences were observed in amplitude and peak velocity of flexor and extensor. There was a significant group x time interaction with the older group demonstrating a progressive increase in muscle activation pattern (e.g., co-contraction) over time while the younger group maintained their initial levels relatively constant. There was an interaction with peak velocity of the extensor muscle whereby the young decreased at a faster rate than the older group. With respect to the non-dominant index finger, the median frequency of the extensor was different between groups with the young experiencing a leftward shift indicative of fatigue. The young group declined in maximal velocity of the extensor as well as the pre-post difference in maximal voluntary contraction of the extensor. Although the young group exhibited signs of peripheral fatigue on the non-dominant side only, there were no signs of peripheral fatigue on either side of the older group. We conclude that the chosen MVR task challenges the central limits of the motor system differently with age, not only in the way that the two groups respond in terms of movement kinematics and patterns of muscle activation but also in the way that elderly appear to pre-program their maximal voluntary movements. We also conclude that hand dominance plays a differential role in the outcome of the MVR task in that the non-dominant side adjusts differently to the MVR in terms of peak velocity and median frequency (extensors) and that the young appear to experience a peripheral form of fatigue that is not seen in the elderly.