Figure 12.

Cosine tuning for synergy amplitude coefficients and for largest muscle bursts. In most cases, the dependence of the synergy amplitude coefficients on the direction of movement was well captured by a cosine function with an offset (see Materials and Methods). The distribution of R² values of the cosine fit over all conditions (3 loads or postures times; 2 endpoints) and synergies (a, top row, light gray bars) had a median, for each subject in experiment 1 (subjects 1–3) and experiment 2 (subjects 4–6), significantly higher than the median of the distribution of the R² values of the cosine fit, over all conditions and muscles, of the amplitude of the largest 100 ms EMG burst (a, bottom row, dark gray bars). Moreover, the preferred direction of the cosine tuning was less variable, across conditions, for the synergies than for the muscles. The distribution of the angular deviations, across load or posture and endpoint conditions, for each synergy and plane of movement (b, top row, light gray bars) had a smaller median than the distribution of the angular deviations for each muscle and plane (b, bottom row, dark gray bars). deg, Degree.