Age-related changes in postural responses preceding rapid self-paced and reaction time arm movements.

The electromyographic responses in postural (thigh and trunk) and primary agonist (shoulder) muscles were examined in standing young and older adults prior to rapid self-paced (SP) and simple reaction time (RT) arm flexion movements. In contrast to younger subjects, older adults demonstrated significantly lower frequencies of trials for self-paced movements in which thigh muscle responses preceded the activation of the shoulder muscle. Furthermore, younger adults showed more frequent early lower limb postural responses for SP versus RT movements, whereas older subjects retained comparable frequencies between task conditions. Overall, a significantly shorter intermuscular timing interval between leg and arm muscle onsets was also found for the older group.