Exp Brain Res (2007) 181:627–637 DOI 10.1007/s00221-007-0959-3 123 RESEARCH ARTICLE Parallels in control of voluntary and perturbation-evoked reach-to-grasp movements: EMG and kinematics William H. Gage · Karl F. Zabjek · Stephen W. Hill · William E. McIlroy Received: 15 July 2006 / Accepted: 12 April 2007 / Published online: 9 May 2007  Springer-Verlag 2007 Abstract To determine the potential diVerences in con- trol underlying compensatory and voluntary reach-to-grasp movements the current study compared the kinematic and electromyographic proWles associated with upper limb movement. Postural perturbations were delivered to evoke compensatory reach-to-grasp in ten healthy young adult volunteers while seated on a chair that tilted as an inverted pendulum in the frontal plane. Participants reached to grasp a laterally positioned stable handhold and pulled (or pushed) to return the chair to vertical. The distinguishing characteristic between the two behaviors was the onset latency and speed of movement. Consistent with compensa- tory balance reactions, the perturbation-evoked reach response was initiated very rapidly (137 vs. 239 ms for vol- untary). As well the movement time was shorter, and peak velocity was greater for PERT movements. In spite of the profound diVerences in timing, the sequence of muscle activity onsets and the order of speciWc kinematic events were not diVerent between maximum velocity voluntary (VOL) and perturbation-evoked (PERT) reach-to-grasp movements. Peak velocity and grasp aperture occurred prior to hand contact with the target for PERT and VOL movements, and wrist trajectory was inXuenced by the direction of perturbation relative to the target. To achieve such target speciWc control for responses initiated within 100 ms of the perturbation, and when characteristics of body movement were unpredictable, the perturbation- evoked movements would need to incorporate sensory cues associated with body movement relative to the target into the earliest aspects of the movement. This suggests reliance on an internal spatial map constructed prior to the onset of perturbation. Parallels in electromyographic and kinematic proWles between compensatory and voluntary reach-to- grasp movements, in spite of temporal diVerences, lead to the view they are controlled by common neural mechanisms. Keywords Voluntary reaching · Aperture control · Compensatory balance control · Postural perturbation Introduction Both upper and lower limb use for stepping and/or grasping to reestablish stability following balance perturbations has been recognized as an essential class of behaviours used to maintain upright stability, and referred to as change-in-support reactions (Maki and McIlroy 1997; Maki et al. 2003). While previous research has explored the control of the lower limbs and the trunk in the temporal and spatial organization of the balance response (Maki et al. 1996; W. H. Gage · K. F. Zabjek · S. W. Hill · W. E. McIlroy Toronto Rehabilitation Institute, 550 University Avenue, Toronto, ON Canada, M5G 2A2 K. F. Zabjek · W. E. McIlroy Graduate Department of Rehabilitation Science and Department of Physical Therapy, University of Toronto, 500 University Avenue, Toronto, ON Canada, M5G 2A2 W. H. Gage · K. F. Zabjek · S. W. Hill · W. E. McIlroy Heart and Stroke Centre for Stroke Recovery, Sunnybrook and Womens’ College Health Sciences Centre, 2075 Bayview Avenue, Toronto, ON Canada, M4N 3M5 W. H. Gage (&) School of Kinesiology and Health Science, York University, 4700 Keele Street, Toronto, ON Canada, M3J 1P3 e-mail: whgage@yorku.ca W. E. McIlroy Department of Kinesiology, University of Waterloo, 200 University Avenue, Waterloo, ON Canada, N2L 3G1