A higher-order mechanism overrules the automatic grip-load force constraint during bimanual asymmetrical movements

The aim of the present study was to examine grip-load force regulation duri ng unimanual and bimanual movements. Two protocols were included which mani pulated the object's weight and covered distance. Results showed that grip- load ratio was adapted to the task requirements. During unimanual and biman ual symmetrical movements, an increased grip-load force ratio for long vers us short amplitude movements as well as for light versus heavy weight movem ents was noted. These findings could be related to the observed movement sp eed variations associated with the tasks. During bimanual asymmetrical move ments, the grip-load force ratio became comparable for both sides. When tra nsporting different object's weights to constant distances, the grip-load f orce ratio of light weight movements decreased towards that of heavy weight movements. As movement speed was reduced, it indicates that grasping force s were adapted accordingly. When transporting constant object's weights to different distances, the grip-load force ratio of short amplitude movements increased towards that of long amplitude movements. Since movement speed w as decreased, it suggests that a bimanual coordinative command overruled th e automatic grip-load coupling. In conclusion, these data show that interli mb coupling induced a rescaling towards a common control structure, leading to similar grasping forces during bimanual movements with dissimilar actio ns. (C) 2001 Elsevier science B.V. All rights reserved.