Anticipatory postural adjustments in forward and backward single stepping: Task variability and effects of footwear

A single step is usually preceded by the so-named anticipatory postural adjustments (APAs). These are normally described through the observation of the trajectory of the center of pressure (CoP). Even though, external factors such as stepping direction and footwear are known to modify APAs, quantitative investigations regarding their relevant effects are understudied in the literature. Therefore, this study aims at characterizing APAs patterns prior to forward and backward stepping when performed either in barefoot or shod condition and explores their variability. Twenty-eight young healthy volunteers participated in the study. CoP trajectories were recorded using a force plate and relevant spatio-temporal parameters extracted (i.e. duration, amplitude, and mean speed). Results showed distinct effects of both direction of the step and footwear on APAs: the first mainly induces variations of APAs along the anteroposterior direction, whereas the latter in the mediolateral direction. In addition, variability indices exhibited lower values for the APAs along the mediolateral axis which was affected by neither footwear nor direction of the step. This study extends previous literature by revealing significant direction X footwear interactions on APAs. Furthermore, regardless of these factors, the medio-lateral strategy is still well preserved, highlighting the prioritization of balance control over motor performance. In conclusion, both direction and footwear have a major effect on postural preparation therefore both factors should be included when evaluating APAs in real-life condition.