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Effects of Gait Variations on Grip Force Coordination During Object Transport

¹Department of Biobehavioral Sciences, Teachers College and ⁴Department of Rehabilitation Medicine, College of Physicians and Surgeons, Columbia University, New York City, New York; ²Department of Applied Physiology and Kinesiology, University of Florida, Gainesville, Florida; and ³Institute of Human Movement Sciences and Sport, ETH Zurich, Switzerland

Submitted 15 May 2008; accepted in final form 21 August 2008

In object transport during unimpeded locomotion, grip force is precisely timed and scaled to the regularly paced sinusoidal inertial force fluctuations. However, it is unknown whether this coupling is due to moment-to-moment predictions of upcoming inertial forces or a longer, generalized time estimate of regularly paced inertial forces generated during the normal gait cycle. Eight subjects transported a grip instrument during five walking conditions, four of which altered the gait cycle. The variations included changes in step length (taking a longer or shorter step) or stepping on and over a stable (predictable) or unstable (unpredictable support surface) obstacle within a series of baseline steps, which resulted in altered frequencies and magnitudes of the inertial forces exerted on the transported object. Except when stepping on the unstable obstacle, a tight temporal coupling between the grip and inertial forces was maintained across gait variations. Precision of this timing varied slightly within the time window for anticipatory grip force control possibly due to increased attention demands related to some of the step alterations. Furthermore, subjects anticipated variations in inertial force when the gait cycle was altered with increases or decreases in grip force, relative to the level of the inertial force peaks. Overall the maintenance of force coupling and scaling across predictable walking conditions suggests that the CNS is able to anticipate changes in inertial forces generated by gait variations and to efficiently predict the grip force needed to maintain object stability on a moment-to-moment basis.

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