Citation

Cappellini G, Ivanenko YP, Dominici N, Poppele RE, Lacquaniti F. J. Neurophysiol. 2010; 103(2): 746-760.

Affiliation

IRCCS Fondazione Santa Lucia.

Copyright

(Copyright © 2010, American Physiological Society)

DOI

10.1152/jn.00499.2009

PMID

19955283

Abstract

Friction and gravity represent two basic physical constraints of terrestrial locomotion that affect both motor patterns and the biomechanics of bipedal gait. To provide insights into the spatiotemporal organization of the motor output in connection with ground contact forces, we studied adaptation of human gait to steady low friction conditions. Subjects walked along a slippery walkway (7-m-long, friction coefficient ~0.06) or a normal, non-slippery floor at a natural speed. We recorded gait kinematics, ground reaction forces and bilateral electromyographic (EMG) activity of 16 leg and trunk muscles, and we mapped the recorded EMG patterns onto the spinal cord in approximate rostrocaudal locations of the motoneuron (MN) pools to characterize the spatiotemporal organization of the motor output. The results revealed several idiosyncratic features of walking on the slippery surface. The step length, cycle duration and horizontal shear forces were significantly smaller, the head orientation tended to be stabilized in space while arm movements, trunk rotations and lateral trunk inclinations considerably increased, and foot motion and gait kinematics resembled those of a non-plantigrade gait. Furthermore, walking on the slippery surface required stabilization of the hip and of the centre-of-body-mass in the frontal plane, which significantly improved with practice. Motor patterns were characterized by an enhanced (~2-fold) level of MN activity, substantial decoupling of anatomical synergists and the absence of systematic displacements of the centre of MN activity in the lumbosacral enlargement. Overall, the results show that when subjects are confronted with unsteady surface conditions, like the slippery floor, they adopt a gait mode that tends to keep the COM centered over the supporting limbs and to increase limb stiffness. We suggest that this behavior may represent a distinct gait mode that is particularly suited to uncertain surface conditions in general.

Language: en