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How Quickly Can Healthy Adults Move Their Hands to Intercept an Approaching Object? Age and Gender Effects

^a Department of Mechanical Engineering, University of Michigan, Ann Arbor
^b Department of Biomedical Engineering, University of Michigan, Ann Arbor
^c Institute of Gerontology, University of Michigan, Ann Arbor
^d Department of Internal Medicine, University of Michigan, Ann Arbor
^e Ann Arbor VA Medical Center GRECC, Michigan

James A. Ashton-Miller, University of Michigan, MEAM, GGB 3208, Ann Arbor, MI 48109-2125 E-mail: jaam{at}umich.edu.

Decision Editor: John E. Morley, MB, BCh

Background. The upper extremities are often used to protect the head and torso from impact with an object or with the ground. We tested the null hypotheses that neither age nor gender would affect the time required for healthy adults to move their upper extremities into a protective posture.

Methods. Twenty young (mean age 25 years) and twenty older (mean age 70 years) volunteers, with equal gender representation, performed a seated arm-movement task under three conditions: Condition 1, in which subjects were instructed to raise the hands upon cue as quickly as possible from thigh level to a shoulder height target; Condition 2, in which subjects were instructed as in Condition 1 with the addition of intercepting a swinging pendulum at the prescribed hand target; and Condition 3, in which subjects were instructed as in Condition 2 but were asked to wait as long as possible before initiating hand movement to intercept the pendulum. Arm movements were quantified using standard kinematic techniques.

Results. Age (p < .01) and gender (p < .05) affected hand movement times. In Conditions 1 and 2, the older women required 20% longer movement times than the other subject groups (335 vs 279 milliseconds; p < .01). In Condition 3, shorter movement times were achieved by young men (20%; p = .002) and older women (10%; p = .056) as compared with their respective performance in Conditions 1 and 2 because they did not fully decelerate their hands. The other groups slowed their movements in Condition 3.

Conclusions. Age, gender, and perceived threat significantly affected movement times. However, even the slowest movement times were well within the time available to deploy the hands in a forward fall to the ground.

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