Figure 2.

Relationship between musculoskeletal model, controller, and simulator. The controller takes as input the simulation state (body position, joint configuration, contact state, etc.), denoted by s and outputs neural excitation signals (u) and torques (τ̃). Excitation signals are converted to muscle activations (a), which are then converted to torques τ for the hip, knee, and ankle sagittal DOFs. The remaining DOFs are directly actuated by τ̃. The excitation to torque mapping is a function of the contractile element kinematics (l^CE, v^CE) and hip, knee, and ankle joint configuration (θ).