Details on Subjects and Experimental Trials used for Regression Fits.

: Body weight (kg), and : Body height (m). and : Minimum and maximum gait speed (m/s). and : Minimum and maximum quasi-stiffness in dorsi-flexion phase (Nm/rad). and : Minimum and maximum quasi-stiffness in dual flexion phase (Nm/rad). and : Minimum and maximum quasi-stiffness in plantar-flexion phase (Nm/rad). and : Minimum and maximum propulsion energy (J). , , and : Average of the linear fit on moment-angle curve in dorsi-flexion, dual-flexion, and plantar-flexion phases. ‡Data collected at Human PoWeR Lab, NC State University [28]. †Data collected at Biomechanics Lab, East Carolina University [43]. •Data collected at Laboratory of Biomedical Technologies at Politecnico Di Milano.