Does the location of the touch from the contralateral finger application affect grip force control while lifting an object?

It was recently shown that the magnitude of grip force used to lift and transport a hand-held object decreased if a light finger touch from the contralateral arm was provided to the wrist of the target arm [A.S. Aruin, Support-specific modulation of grip force in individuals with hemiparesis, Arch. Phys. Med. Rehabil. 86 (2005) 768-775]. In this study, we investigated whether the location of the finger touch along the target arm affects the way grip force is reduced. Subjects performed the same task of lifting and transporting an instrumented object with no involvement of the contralateral arm and when an index finger touch of the contralateral arm was provided to the wrist, thumb, mid-forearm, and the hand-held object. Grip force was reduced by approximately the same amount in all conditions with the finger touch compared to the no touch condition suggesting that its reduction was not associated with a particular point of contact of the finger with the target arm. The results of the study provide additional evidence to support of the use of a second arm in the performance of activities of daily living and stress the importance of future studies investigating contralateral arm sensory input on grip force control.