The intentional on-line adaptive capabilities of human movements during continuous variation in gravitational force were investigated. Subjects performed rhythmic forearm movements in the gravitational plane during parabolic flight maneuvers that induced a continuous change from 1.8 G to 0 G over a period of 2.3 s. During the initial plateau of hypergravity, subjects produced movements at two frequencies, with and without space constraints. Afterward, they were faced with the drop in gravity, during which they were instructed either to let the movement evolve freely while maintaining the initial frequency (time-constrained task) or to intentionally maintain the frequency, amplitude, and forearm center of oscillation (time/space-constrained task). The results showed (a) a reduced angle for the forearm center of oscillation and maintenance of movement amplitude in the time-constrained task, (b) a change from an in-phase to an out-of-phase biceps/triceps activation pattern regardless of the task, and (c) an earlier occurrence of this change in the time/space-constrained task, impeding the spontaneous forearm rise. These results are discussed in the perspective of the λ model.
The authors are with “Mouvement et Perception” UMR 6559, Université de la Méditerranée, CNRS, Faculté des Sciences du Sport, 163 Avenue de Luminy CP910, 13288 Marseille Ced. 9, France.