Effects of age and fine motor expertise on the bilateral deficit in force initiation.

Performance of a task carried out with two hands separately is better than the performance of the same task done with both hands at the same time. This so-called bilateral deficit may be reduced or counteracted by long-term practice. Little is known about age-related changes. We examined age- and expertise-related differences in the bilateral deficit in force initiation. Participants performed static and dynamic force modulation tasks either with the right and left hand separately or both hands simultaneously. In order to examine age-related differences, we compared novices of fine motor control (service employees) from three age groups, covering the working age (young n = 13, early middle-aged n = 10 and late middle-aged n = 12). To assess the influence of expertise, we considered precision mechanics as experts in fine motor control. To ensure the acquisition of expertise, only early middle-aged (n = 10) and late middle-aged (n = 14) experts were recruited. Regardless of the task, bimanual force initiation was slower than unimanual force initiation. This bilateral deficit was (1) more pronounced in the static than in the dynamic task, (2) higher in early and late middle-aged than in younger novices, and (3) lower in experts as compared to novices. Based on our results, we assume both interhemispheric inhibition and division of attention to contribute to the bilateral deficit and the expertise- and age-related differences, respectively. The results are promising for the possibility to overcome constraints of bilateral hand movements by long-term practice.