Fig. 1.

Human elbow actuation. a Elbow anatomy. b Simulation of an elbow composed of three bones (humerus, ulna and radius) and two heads of biceps (short and long head) performing a complete flexion. c Experimental data⁶⁰ and simulations for active and passive force normalized with peak force $\left(F_{\mathrm{m}}∕F_{\max }\right)$ during the isometric exercise ($F_{\mathrm{set}}$ mimics the resistance encountered by the muscle and results in its equilibrium length $\eta$). d Experimental⁶¹ and simulation torque measurements of the elbow joint (angled at 60°) performing maximal isokinetic concentric flexions at different angular velocities along with the corresponding overall muscle strain rate damping $\zeta$. The numerically determined $\zeta$ (see Supplementary Note 2) are then compared with theoretical estimates based on the Hill model⁶²