Figure 2. The impact of context changes on kinematics and muscle activation.

(A) Trial-averaged traces of index finger position and index finger flexion velocity for an example 1-degree-of-freedom (1-DOF) spring session with Monkey N. Trials are aligned to peak movement (vertical gray line). Black traces are normal trials, blue are trials with springs in the manipulandum, solid traces are for flexion trials, and dotted traces are for extension trials. Shaded area shows one standard deviation. (B) Trial-averaged traces of flexor digitorum profundus (FDP) muscle activation and extensor digitorum communis (EDC) muscle activation for an example spring session with Monkey N. Formatted the same as (A). (C) Change in peak velocity between normal trials and trials with either springs present or the wrist flexed for both Monkey N (left) and Monkey W (right). Trials are split by movement direction, either flexion or extension. Error bars indicate 99% confidence interval based on a two-sample t-test. (D, E) Change in average muscle activation in a window around peak movement between normal trials and trials in the spring (blue) or wrist context (yellow) for all eight muscles recorded in Monkey N. Trials are split between flexion (D) and extension (E) movements. Error bars indicate 99% confidence interval based on a two-sample t-test.