A. E. Kerdok, A. A. Biewener, T. A. McMahon, P. G. Weyand, and H. M. Herr. Energetics and mechanics of human running on surfaces of different stiffnesses, Journal of Applied Physiology, vol. 92, no. 2, pp. 469-478, 2002.
J. Blaya and H. M. Herr. Adaptive control of a variable-impedance ankle-foot orthosis to assist drop-foot gait, IEEE Transactions on Neural Systems & Rehabilitation Engineering. vol. 12, no. 1, pp. 24-31, 2004.