title: Effects of linear movements on upright standing position.
abstract: This study investigated the effects of antero-posterior movement on the upright standing posture in the humans. Subjects were asked to stand on a platform in a linear accelerator (sled) in the dark. At a fixed distance of sled movements in an antero-posterior direction, peak speed was changed by sinusoidal modes run at 0.02 G, 0.04 G, 0.06 G and 0.08 G. At lower speeds (0.02 G and 0.04 G) joints moved in parallel, but at higher speeds (0.06 G and 0.08 G) the hip flexed or extended in the direction of the sway. At lower speeds (0.02 G and 0.04 G) EMG in lower leg exhibited co-activated patterns in both forward and backward accelerations at lower speeds (0.02 G and 0.04 G), but at higher speeds (0.06 G and 0.08 G) TA was activated with reciprocal inhibition of GC to maintain the body in equilibrium in a reflexive manner. This reciprocal inhibition may be due to main reflex control elicited by motor functions as a result of the linear acceleration. The threshold of speed was assumed to be from 0.04 G to 0.06 G for all but one subject.
authors.affiliation: Space Medicine Research Center, Research Institute of Environmental Medicine, Nagoya University, Nagoya.
authors.forename: O
authors.initials: O
authors.lastname: Kawakami
authors.forename: H
authors.initials: H
authors.lastname: Sudoh
authors.forename: S
authors.initials: S
authors.lastname: Watanabe
mesh_terms: D000054:Acceleration; D000328:Adult; D000842:Ankle; D004576:Electromyography; D006257:Head; D006615:Hip; D006801:Humans; D007717:Knee; D007866:Leg; D009068:Movement; D018482:Muscle, Skeletal / Q000502:physiology*; D004856:Postural Balance / Q000502:physiology*; D011187:Posture / Q000502:physiology*