Compensatory mechanisms of balance to the scaling of arm-swing frequency

The present study investigated the contribution of the Hof (2007) mechanism 1 (M1-moving the center of pressure (COP) with respect to the vertical projection of the center of mass (COMTotal:)); and mechanism 2 (M2-rotating the trunk and upper limbs around the COMTotal) to control and the stability of COP-COMTotal cophase as a function of lateral arm-swing frequency. Young adults were instructed to stand still on a force platform while alternating their arm swinging from above the head to the side of their thigh to create perturbations to postural control. Scaling the frequency of arm-swing (random step changes of 0.2 Hz within a bandwidth of 0.2 to 1.6 Hz) increased the SD of COP but decreased the SD of COMTotal. Increments in arm-swing frequency induced a progressive increase in M1 and decrease in M2 in terms of their relative contribution to postural stability. The cophase between COP and COMTotal became more tightly in-phase over increments of arm-swing frequency. These findings show an adaptive compensatory role of M1 and M2 within the stability of COP-COMTotal coupling in the regulation of human balance control. (C) 2015 Elsevier Ltd. All rights reserved.We gratefully acknowledge the generous advice and technical support from Dr. At L. Hof at Laboratory of Human Movement Analysis, Center of Rehabilitation of University Medical Center Groningen (Netherlands)