Behavior of simplified mechanical model over the gait cycle. The model was optimized to reproduce knee moment, T_req, of a prosthetic leg with a typical inertial configuration (mass of upper leg = 50% of able-bodied value, and masses of lower leg and foot = 33% of able-bodied values). (a) Illustration of optimized engagement (θ_eng) and disengagement (θ_dis) angles of the clutch for each component. (b) Comparison of knee moment normalized to body mass for normative kinematics (⁠$Treq*$⁠) and produced by the mechanical model (⁠$Tmod*$⁠). Agreement between $Treq*$ and $Tmod*$ is $R2=0.90$⁠. Labels k₁ and b₀ designate the linear spring coefficient and constant damping coefficient for a given phase. Note that the difference between $Tmod*$ and $Treq*$ around 45% of the gait cycle is a consequence of a negative work, W_neg, to positive work, W_pos, ratio of less than one during phase 1, meaning that more energy is generated than dissipated (Fig. 4). Thus, a single passive mechanical component cannot perfectly reproduce T_req during phase 1. (c) Comparison of knee power (normalized to body mass) required for normative kinematics and knee power produced by the mechanical model. Knee power is calculated as the product of knee moment (modeled or required) and able-bodied angular velocity of the knee joint. Agreement between required knee power and modeled knee power is $R2=0.91$⁠. Hatched areas show where the modeled knee power is insufficient and is less than the generative knee power required for normative gait kinematics.