Alterations in the intersegmental coordination of landing from a jump in a microgravity environment.

The objective is to investigate the intersegmental coordination during landing from a countermovement jump in different gravitational environments to gain insight on how humans perceive gravity and coordinate complex motor tasks. Eight participants performed countermovement jumps on Earth (1 g) and while submitted to four simulated gravity levels (from 0.2 to 1 g) generated by a downward pull-down force in weightlessness induced by parabolic flights. The orientation of body segments (i.e., elevation angles) was recorded using a high-speed camera. A principal component analysis was performed on the elevation angles of the foot, shank, thigh, and trunk segments together with a correlation analysis. Regardless of the environment, the movements of the four body segments are tuned through a law of intersegmental coordination; the vertical position of the center of mass of the body being identified as the parameter controlled. The movement of the foot seems an independent factor, given its minimal contribution to the intersegmental coordination and the poor correlation with the shank segment. In weightlessness, the intersegmental coordination is less unidimensional and more variable compared with Earth's gravity. In addition, the lower the gravity level simulated in weightlessness, the greater the contribution of the foot and of the shank, and the lower the contribution of the thigh, suggest an adjustment of the intersegmental coordination through a reweighting of altered sensory inputs. In conclusion, the intersegmental coordination remains better optimized for Earth gravity, but the unidimensional synergy is preserved in weightlessness when using a downward pull-down force to simulate gravity.NEW & NOTEWORTHY During landing, the movements of the trunk, thigh, shank, and foot are tuned through a unidimensional synergy, identified as the vertical position of the center of mass. In microgravity, the coordination is overall less unidimensional and more variable compared with Earth's gravity, suggesting a suboptimal coordination. In lower microgravity levels, greater contribution of the foot and of the shank, and lower contribution of the thigh suggest an adjustment through a reweighting of sensory inputs.