Normal aging reduces motor synergies in manual pointing

Left: Setup and marker placement in start position. Note that the targets were placed in front of the left shoulder, thus the required movement trajectory was diagonally left and upward. Right: Illustration of the segmentation procedure. Cartesian 3-dimensional position data (top) and tangential velocity (bottom) of the finger tip. First, the main section of the pointing movement was determined as the interval during which the tangential velocity was above 10% of the peak velocity. Based on this, 5 time points of the movement (start, early, middle, late, and end) were determined. See text for more details.

Joint angle excursions (maximum minus minimum) during the pointing movement, for each joint angle and the 2 age groups. Significant differences between the age groups are indicated by stars (Welch's 2-sample t test; *p < 0.05, **p < 0.01, ***p < 0.001). Error bars represent standard error of the mean (SEM).

Results of the uncontrolled manifold (UCM) analysis as a function of movement phase and age group. (A) Goal-equivalent and nongoal-equivalent variability (GEV, NGEV). (B) UCM index (log₁₀[GEV/NGEV]; see text). In (B) significant differences between the age groups are indicated by stars (Welch's 2-sample t test; *p < 0.01, **p < 0.001, ***p < 0.0001). Error bars represent standard error of the mean (SEM).