The Biomechatronics Group uses a data-driven approach to study the mechanics and control of human running, with the goal of applying the findings to hardware control.
Swing-leg retraction: a simple control model for stable human running
In running, the spring-like axial behavior of stance limbs is a well-known and remarkably general feature. Here we consider how the rotational behavior of limbs affects running stability. It is commonly observed that running animals retract their limbs just prior to ground contact, moving each foot rearward towards the ground. In this study, we employ a conservative spring-mass model to test the effects of swing-leg retraction on running stability. A feed-forward control scheme is applied where the swing-leg is retracted at constant angular velocity throughout the second half of the swing phase. The control scheme allows the spring-mass system to automatically adapt the angle of attack in response to disturbances in forward speed and stance-limb stiffness. Using a return map to investigate system stability, we propose an optimal swing-leg retraction model for the stabilization of flight phase apex height. The results of this study indicate that swing-leg retraction significantly improves the stability of spring-mass running, suggesting that swing-phase limb dynamics may play an important role in the stabilization of running animals.
A. Seyfarth, H. Geyer, and H. M. Herr.
Swing-leg retraction: a simple control model for stable running,
Energetics and mechanics of human running on surfaces of different stiffnesses
Mammals use the elastic components in their legs (principally tendons, ligaments, and muscles) to run economically, while maintaining consistent support mechanics across various surfaces. To examine how leg stiffness and metabolic cost are affected by changes in substrate stiffness, we built experimental platforms with adjustable stiffness to fit on a force-plate-fitted treadmill. Eight male subjects [mean body mass: 74.4 7.1 (SD) kg; leg length: 0.96 0.05 m] ran at 3.7 m/s over five different surface stiffnesses (75.4, 97.5, 216.8, 454.2, and 945.7 kN/m). Metabolic, ground-reaction force, and kinematic data were collected. The 12.5-fold decrease in surface stiffness resulted in a 12% decrease in the runner’s metabolic rate and a 29% increase in their leg stiffness. The runner’s support mechanics remained essentially unchanged. These results indicate that surface stiffness affects running economy without affecting running support mechanics. We postulate that an increased energy rebound from the compliant surfaces studied contributes to the enhanced running economy. biomechanics; locomotion; leg stiffness; metabolic
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,
J. App. Phys., 2002.