Force Coordination in Object Manipulation

Purpose: The purpose of this review is to present our recent findings related to the studies of hand function based on the coordination of forces exerted against hand-held objects. Basic procedures: A novel device has been developed for recording grip (GF; acting perpendicu-larly at the hand-object contact) and load force (LF; acting tangentially) during uni- and biman-ual manipulation tasks performed under either static or dynamic conditions. Both healthy partici-pants and neurological patients were tested. The outcome measures were obtained from the task performance (i.e., the ability to exert accurate LF profiles), GF-LF coordination and GF modula-tion. Main findings: The method applied proved to not only to be both reliable and valid, but also suffi-cient to detect differences between the dominant and non-dominant hand, as well as between healthy participants and mildly involved neurological patients. Marked differences in most of the depended variables were also detected between unidirectional and bi-direction tasks (i.e., in the tasks where LF acts in one and in two alternating directions). The later finding could not be based neural mechanisms known for their role in manipulative actions, such as on employing ad hoc muscle synergies or on the afferent activity of skin mechanoreceptors. Conclusions: The employed methodological approach can be applied not only to explore various manipulation activities, but also to serve as a basis for future development of specific clinical tests for populations that demonstrate impaired hand function.