Pushing Induced Sliding Perturbation Affects Postural Responses to Maintain Balance Standing

Pushing is considered a manual handling activity in industry and its functional role is also in our daily life, such as pushing moving strollers or grocery carts, which is under examined. In such situations, two perturbations need to be handled simultaneously, specifically, pushing (voluntary movement) and pushing-induced slipping when walking on a slip surface (sliding perturbation). Eight participants were instructed to push a handle while standing on a locked or unlocked movable board, which was placed on a force plate. Three accelerometers were attached to the handle to detect the moment of the handle moving away (Thandle), which denotes time zero, the pelvis to detect the moment of trunk movement, and the movable board to detect the moment of board movement. The onset time, magnitude of center of pressure (COP) at Thandle and maximum pushing force were calculated. The onsets of board movement, trunk movement, and COP were initiated prior to Thandle. Pushing while standing on the unlocked sliding board significantly affected the onset of COP but did not affect onset of trunk movement. In addition, the direction of acceleration on the board was corresponding to the reaction force of the pushing forces at hands in the backward direction. Studying the combined effects of varying movability of the support surface and pushing tasks may contribute to the development of new environment safety for workers and elderly.