CONTROL OF ISOMETRIC FORCE IN HYPERGRAVITY

Background: Previous work suggests that proprioceptive signals are deg raded in hypergravity (hyper-G). We therefore, expected that productio n of finely graded force is disturbed as well. Method: Subjects produc ed isometric force with their thumb and index finger upon verbal instr uction, before, during, and after exposure to +1.5 Gz and +3 Gz. Produ ced force was orthogonal to the direction of gravity. Results: In hype r-G, responses to a given target value were significantly higher (by a bout 400 pond) than in normal gravity, while the modulation of produce d force with target force didn't change. The results in +1.5 Ct and +3 Gz were quantitatively similar, and a positive aftereffect was found. Conclusions: Subjects underestimate by a constant amount the force the y produce in hyper-G. Our results are reminiscent of similar findings with pointing and grasping movements in hyper-G.