Fig. 6

Relationship between lower-limb neuromechanics and whole-body metabolic rate. The relationships between changes in ankle joint and muscle-level neuromechanical rate metrics (x) and the change in net metabolic rate (J s^− 1 kg^− 1) (y) during walking with exoskeletons over a range of walking speeds and stiffness values, k_exo. For each metric, Δ represents the difference from the k_exo = 0 condition (i.e., the effect of increasing exoskeleton stiffness) with positive values indicating an increase. We used a within-participant linear regression analysis to determine whether relationships were significant (*p < 0.05), and we report the line of best fit to the data and the R² value of the fit. Statistics on the lines of best fit are also reported in Table 1. Note that work rate (J s^− 1) and power (W) are synonymous