Effects of Gravity on Multi-digit Torque Production Task in Humans

In this study we investigated the effect of gravity on multi-digit prehension to know how the digits’ force and moment are organized in the imposed static constraints according to the gravity. Specifically, we tested if decoupling of grasping and rotational equilibrium control is even valid during grasping in the microgravity condition. There were two experimental conditions: gravity-induced (GI), and microgravity conditions (MG). For the MG condition, the handle was attached to the end of the robot-arm, which produced a count-balanced force for the weight of the handle and hand. The results showed that the selected experimental variables were separated into two sub-sets in both GI and MG conditions. Thus, we can conclude that the grasping stability is independent from the rotational equilibrium control regardless of the gravity acting on the hand-held object.