Elastic energy savings and active energy cost in a simple model of running
Fig 9
Energetic cost of running vs. ground slope for unified Actuated Spring-mass model.
(A) Model Cost of Transport (solid line) compared to humans (circles; [11]). Also shown are asymptotes (thin lines) for muscle efficiency of positive and negative mechanical work (25% and -120%, respectively). (B) Contributors to model Cost of Transport: positive work cost, negative work cost, force-rate cost ER, and a constant offset. Parameter sensitivities are included for varying (C) stiffness k, (D) force-rate coefficient ε, (E) hysteresis (damping ratio ζ), and (F) collision fraction CF. Each trace indicates variation from lowest to highest parameter values: k ranging 13.7 kN m-1 –∞, ε ranging 0–2∙10−3, ζ ranging 0–0.2, CF ranging 0–0.06. All model results are for nominal running at speed of 3 m s-1 and step frequency of 2.94 Hz.