Figure 2

Flowchart of the optimal FRO stiffness selection procedure. After sorting the different stiffness configurations based on peak knee extension angle in single support (KE-K_x), absolute differences in peak KE will be calculated. KE-K₂ and/or KE-K₃ will be excluded if this difference is more than five degrees. Otherwise, the remaining configurations will be sorted by net non-dimensional walking energy cost (NNC-K_x) (this can be either two or three remaining configurations). The stiffness that results in the lowest walking energy cost will be selected as the subject’s optimal FRO. K_1, K₂ and K₃ = rigid, stiff, or flexible FRO stiffness configurations; K_OPT = subject’s optimal FRO stiffness; KE = knee extension angle; KE-K_x = stiffness sorted by KE; NN_cost_%SMC = net non-dimensional walking energy cost relative to speed matched controls; NNC-K_x = stiffness sorted by NN_cost_%SMC; SS = single support.