Recovery responses to surrogate slipping tasks differ from responses to actual slips

Slipping and slip-related falls are a common and potentially dangerous problem, especially for older adults. We believe that it is possible to train compensatory stepping responses of older adults to reduce the incidence of slip-related falls. However, such an approach requires further understanding of the causal biomechanical distinctions between a successful and an unsuccessful recovery effort. Surrogate tasks are often used to study complex biomechanical events associated with large postural disturbances. Although surrogate tasks enhance experimental control over one or more elements of a generally more complex event, such control may change the task of interest by imposing biomechanical constraints that reduce the validity of the surrogate. The purpose of the present study was to quantify the differences in lower extremity and trunk kinematics following a simulated slip versus an actual slip. We hypothesized that the simulated slips would be less variable than real slips and would result in significantly different, and less realistic recovery kinematics. Twenty-two healthy young adults were subjected to unexpected slips using a custom slipping platform and artificial ice. Biomechanical variables associated with the slipping foot were significantly less variable in those slips induced with the platform compared to slips induced with the artificial ice. Significant differences between successful and unsuccessful recovery efforts were found for lower extremity and trunk kinematics on both types of slipping surface. Notably, 40% of the variables for which between surface differences were significant were also those variables that distinguished successful and unsuccessful recovery efforts on the two surfaces. The results suggest that slips induced using artificial ice more accurately reflect the type of slips that occur in the community.