caa a22 4500 445352450 CHVBK 20180317142848.0 cr unu---uuuuu 170323e20110901xx s 000 0 eng 10.1007/s00221-011-2799-4 doi (NATIONALLICENCE)springer-10.1007/s00221-011-2799-4 Prehension synergies during smooth changes of the external torque [Elektronische Daten] [Yao Sun, Jaebum Park, Vladimir Zatsiorsky, Mark Latash] We studied characteristics of digit action and their co-variation patterns across trials (prehension synergies) during static holding of an object while the external torque could change slowly and smoothly. The subjects held in the air an instrumented handle with an attachment that allowed a smooth change in the external torque over about 12s; the load was always kept constant. Series of trials were performed under three conditions: The torque could be zero throughout the trial, or it could change slowly requiring a smooth change of the effort from a non-zero pronation value to zero (PR-0) or from a non-zero supination value to zero (SU-0). The handle was kept vertical at all times. Indices of variance and co-variation of elemental variables (forces and moments of force produced by individual digits) stabilizing such performance variables as total normal force, total tangential force, and total moment of force were computed at two levels of an assumed control hierarchy. At the upper level, the task is shared between the thumb and virtual finger (an imagined digit with the mechanical action equal to that of the four fingers), while at the lower level, the action of the virtual finger is shared among the actual four fingers. We analyzed the total moment of force as the sum of the moments of force produced by the thumb and virtual finger and also as the sum of the moments of force produced by the normal forces and tangential forces. The results showed that the adjustments in the total moment of force were produced primarily with changes in the moment produced by the virtual finger and by changes in the moment produced by the normal forces. The normal force of the thumb at the final state (which was the same across conditions) was larger in the two conditions with changes in the external torque. The safety margin was significantly higher in the PR-0 condition, and it dropped with the decrease in the external torque. A co-contraction index was computed to reflect the moment of force production by the fingers acting against the total moment produced by the virtual finger. It was higher for the SU-0 condition. Most variance indices dropped with a decrease in the external torque. The co-variation indices, however, remained unchanged over the trial duration. They showed signs of a trade-off between the two levels of the assumed hierarchy: larger indices at the higher level corresponded to smaller indices at the lower level. This study and the previous one (Sun et al. in Exp Brain Res 209:571-585, 2011) document several previously unknown features of prehensile tasks. The results show that characteristics of digit action and interaction in such tasks depend not only on the magnitudes of external constraints but also on a variety of other factors including time changes in the constraints and their history. Springer-Verlag, 2011 Prehension nationallicence Safety margin nationallicence Synergy nationallicence History effects nationallicence Sun Yao Department of Kinesiology, The Pennsylvania State University, Rec. Hall-268N, 16802, University Park, PA, USA aut Park Jaebum Department of Kinesiology, The Pennsylvania State University, Rec. Hall-268N, 16802, University Park, PA, USA aut Zatsiorsky Vladimir Department of Kinesiology, The Pennsylvania State University, Rec. Hall-268N, 16802, University Park, PA, USA aut Latash Mark Department of Kinesiology, The Pennsylvania State University, Rec. Hall-268N, 16802, University Park, PA, USA aut Experimental Brain Research Springer-Verlag 213/4(2011-09-01), 493-506 0014-4819 213:4<493 2011 213 221 https://doi.org/10.1007/s00221-011-2799-4 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1007/s00221-011-2799-4 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Sun Yao Department of Kinesiology, The Pennsylvania State University, Rec. Hall-268N, 16802, University Park, PA, USA aut NATIONALLICENCE 700 1- Park Jaebum Department of Kinesiology, The Pennsylvania State University, Rec. Hall-268N, 16802, University Park, PA, USA aut NATIONALLICENCE 700 1- Zatsiorsky Vladimir Department of Kinesiology, The Pennsylvania State University, Rec. Hall-268N, 16802, University Park, PA, USA aut NATIONALLICENCE 700 1- Latash Mark Department of Kinesiology, The Pennsylvania State University, Rec. Hall-268N, 16802, University Park, PA, USA aut NATIONALLICENCE 773 0- Experimental Brain Research Springer-Verlag 213/4(2011-09-01), 493-506 0014-4819 213:4<493 2011 213 221 Metadata rights reserved Springer special CC-BY-NC licence nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer