Figure 5.

Voluntary isometric force to a target level. a, The net reaction force (solid black line) produced by the isometric muscles after optimizing the control inputs to the desired force (dashed black line) using gradient descent algorithm. b, Pulse force trajectory (solid black line) produced after optimizing the control inputs using gradient descent algorithm. c, Agonist (red) and antagonist (blue) motoneuron output for brief rise time (100 ms) pulse-force trajectory. Tasks replicating brief rise time force trajectories (<120 ms) consistently produced antagonistic pulses in both pulse and step force trajectory tasks. d, Agonist (red) and antagonist (blue) motoneuron output for long rise time (250 ms) step-force trajectory task. The antagonist pulse was distinctively absent for intermediate (120–200 ms) and long (>200 ms) rise time force trajectory tasks.