Age-related differences in the stabilization of important task variables in reaching movements

Empirical evidence suggests that the ability to stabilize important task variables of everyday movements by synergistically coordinating redundant degrees of freedom decreases with aging. The aim of the current study was to investigate whether this decrease may be regarded as a characteristic that also applies for the control of multiple task variables. We asked younger and older subjects to repeatedly reach towards and grasp a handle, while joint angle movement of the arm was recorded. The handle constrained final hand position and final hand orientation. Movement variability was analyzed during movement execution by using the uncontrolled manifold method. Results showed that hand orientation was less stabilized in younger than in older subjects. We conclude that aging changes the stability of important task variables. These changes may lead to decreased stability in some task variables, as reported in the literature, but also to increased stability in other task variables.