Comparison of timing and force control of foot tapping between elderly and young subjects.

[Purpose] To examine the ability of young and elderly individuals to control the timing and force of periodic sequential foot tapping. [Subjects and Methods] Participants were 10 young (age, 22.1 ± 4.3 years) and 10 elderly individuals (74.8 ± 6.7 years) who were healthy and active. The foot tapping task consisted of practice (stimulus-synchronized tapping with visual feedback) and recall trials (self-paced tapping without visual feedback), periodically performed in this order, at 500-, 1,000-, and 2,000-ms target interstimulus-onset intervals, with a target force of 20% maximum voluntary contraction of the ankle plantar-flexor muscle. [Results] The coefficients of variation of force and intertap interval, used for quantifying the steadiness of the trials, were significantly greater in the elderly than in the young individuals. At the 500-ms interstimulus-onset interval, age-related effects were observed on the normalized mean absolute error of force, which was used to quantify the accuracy of the trials. The coefficients of variation of intertap interval for elderly individuals were significantly greater in the practice than in the recall trials at the 500- and 1,000-ms interstimulus-onset intervals. [Conclusion] The elderly individuals exhibited greater force and timing variability than the young individuals and showed impaired visuomotor processing during foot tapping sequences.

Interaction interference between arm and leg: division of attention through muscle force regulation.

The first purpose of this study was to examine whether decreases in muscle force similar to the bilateral deficit occur during simultaneous use of arm and leg. The second purpose was to examine the effect on the muscle force of one leg by a division of attention through the regulation of the muscle force in the arm. Six participants completed each of the following three tasks in a random order: (1) maximal unilateral flexion of the right or left elbow, (2) maximal unilateral extension of the left knee, and (3) multilimb effort (a maximal contraction of the muscles in the leg while maintaining a constant submaximal isometric elbow flexion force at 25%, 50%, 75%, or 100% MVC). The results showed that muscle force was lower during simultaneous exertion of arm and leg than during exertion of one limb alone. The maximal knee extension force was significantly (p<.05) lower, by as much as 40% or so, during regulation at 25% MVC. The division of attention is also thought to be involved in task execution and may thus explain the test results. A decrease in the muscle force of the leg due to the level of regulation of the muscle force of the arm indicates that the regulation of the muscle force affects the division of attention, and the finer level of muscle force regulation is a task that requires greater attention. When the muscle force is precisely controlled, a more accurate and more appropriate adjustment is required to focus attention.