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First published online January 30, 2009
Journal of Experimental Biology 212, 523-534 (2009)
Published by The Company of Biologists 2009
doi: 10.1242/jeb.024927

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Control and function of arm swing in human walking and running

Herman Pontzer^1,*, John H. Holloway, 4th¹, David A. Raichlen² and Daniel E. Lieberman³

¹ Department of Anthropology, Washington University, 119 McMillan Hall, Saint Louis, MO 63130, USA
² Department of Anthropology, University of Arizona, 1009 E. South Campus Drive, PO Box 210030, Tucson, AZ 85721, USA
³ Department of Anthropology, Harvard University, 11 Divinity Avenue, Cambridge, MA 02138, USA

^* Author for correspondence (e-mail: hpontzer{at}artsci.wustl.edu)

Accepted 19 November 2008

We investigated the control and function of arm swing in human walking and running to test the hypothesis that the arms act as passive mass dampers powered by movement of the lower body, rather than being actively driven by the shoulder muscles. We measured locomotor cost, deltoid muscle activity and kinematics in 10 healthy adult subjects while walking and running on a treadmill in three experimental conditions: control; no arms (arms folded across the chest); and arm weights (weights worn at the elbow). Decreasing and increasing the moment of inertia of the upper body in no arms and arm weights conditions, respectively, had corresponding effects on head yaw and on the phase differences between shoulder and pelvis rotation, consistent with the view of arms as mass dampers. Angular acceleration of the shoulders and arm increased with torsion of the trunk and shoulder, respectively, but angular acceleration of the shoulders was not inversely related to angular acceleration of the pelvis or arm. Restricting arm swing in no arms trials had no effect on locomotor cost. Anterior and posterior portions of the deltoid contracted simultaneously rather than firing alternately to drive the arm. These results support a passive arm swing hypothesis for upper body movement during human walking and running, in which the trunk and shoulders act primarily as elastic linkages between the pelvis, shoulder girdle and arms, the arms act as passive mass dampers which reduce torso and head rotation, and upper body movement is primarily powered by lower body movement.

Key words: arm swing, walking, running, passive dynamics, tuned mass dampers

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				S. H. Collins, P. G. Adamczyk, and A. D. Kuo Dynamic arm swinging in human walking Proc R Soc B, October 22, 2009; 276(1673): 3679 - 3688. [Abstract] [Full Text] [PDF]

				K. Knight WALKERS SWING ARMS PASSIVELY J. Exp. Biol., February 15, 2009; 212(4): i - ii. [Full Text] [PDF]