The Journal of Neuroscience, April 15, 1999, 19(8):3238-3247
Mechanisms for Age-Related Changes of Fingertip Forces during
Precision Gripping and Lifting in Adults
Kelly J.
Cole ,
Diane L.
Rotella, and
John G.
Harper
Department of Exercise Science, The University of Iowa, Iowa City,
Iowa 52242
We investigated changes across the adult life span of the fingertip
forces used to grip and lift objects and their possible causes. Grip
force, relative safety margin (grip force exceeding the minimum to
avoid slip, as a fraction of slip force), and skin slipperiness
increased beginning at age 50 years. Skin slipperiness explained
relative safety margin increases until age 60 years. Hence, after age
60 years, additional factors must elevate grip force. We argue that one
factor is impaired cutaneous afferent encoding of skin-object
frictional properties on the basis of three findings. First, only
subjects 60 years and older increased their relative safety margins
when the friction of the gripped surfaces was varied randomly versus
experiments that varied only object weight. Skin slipperiness did not
account for this behavior. Second, these older subjects scaled the
initial portion of their force trajectories for the slippery surface
during experiments when friction was varied. Third, their grip force
adjustments to new surfaces were delayed ~100 msec as compared with
young subjects. Previous research has demonstrated that friction is signaled locally by fast-adapting afferents (FA I afferents), which
decrease in number during old age. By contrast, adjustments triggered
by object set-down, an event encoded by FA II afferents throughout the
hand and wrist, were not delayed in our old subjects. Other findings
included that anticipatory control of fingertip forces using memory of
object weight was unimpaired in old age. Finally, old and young adults
modulated their fingertip forces with equal smoothness and with similar
relative intertrial variability.
Key words:
human; prehension; motor control; grasp; hand; cutaneous; age; old; sensory
Copyright © 1999 Society for Neuroscience 0270-6474/99/1983238-10$05.00/0
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