How quickly can healthy adults move their hands to intercept an approaching object? Age and gender effects

Background. The upper extremities are often used to protect the head and tu rso from impact with an object or with the ground. We tested the null hypot heses that neither age nor gender would affect the time required for health y adults to move their upper extremities into a protective posture. Methods. Twenty young (mean age 25 years) and twenty older (mean age 70 yea rs) volunteers. with equal gender representation, performed a seated arm-mo vement task under three conditions: Condition 1, in which subjects were ins tructed to raise the hands upon cue as quickly as possible from thigh level to a shoulder height target, Condition 2, in which subjects were instructe d as in Condition 1 with the addition of intercepting a swinging pendulum a t the prescribed hand target; and Condition 3, in which subjects were instr ucted as in Condition 2 but were asked to wait as long as possible before i nitiating hand movement to intercept the pendulum. Arm movements were quant ified using standard kinematic techniques. Results. Age (p < .01) and gender (p < .05) affected hand movement times. I n Conditions 1 and 2, the older women required 20% longer movement times th an the other subject groups (335 vs 279 milliseconds; p < .01). In Conditio n 3, shorter movement times were achieved by young men (20%; p = .002) and older women (10%; p = .056) as compared with their respective performance i n 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 movem ent times. However, even the slowest movement times were well within the ti me available to deploy the hands in a forward fall to the ground.