Figure 3.

Magnitude and variability of virtual arm neural control signals and virtual muscle forces. The top panels show one-second examples of simulated neural excitation time-histories (A) and resulting virtual muscle force (B) at 20, 40, 60, and 80% of maximal voluntary contraction (MVC) during simulated isometric efforts of the biceps lumped muscle model. The total virtual muscle-tendon length was fixed at 0.3051 m (the length when the virtual arm was at 90° of elbow flexion). The bottom panels show the relationship between the mean and standard deviation (STD) excitation (C) and muscle model force (D) over 10 s at different mean excitation levels from 10 to 100% in 10% increments (100 simulations were performed at each excitation level).