Determinants guiding alternate foot placement selection and the behavioral responses are similar when avoiding a real or a virtual obstacle.

In this study we validate the use of a virtual planar obstacle paradigm to study the avoidance of a real obstacle, such as a hole, during locomotion. Also we further validate the economy determinant implicated with the minimization of foot displacement from its normal landing position during alternate foot placement. Participants were asked to perform two blocks of trials: real (a real hole was embedded in the pathway and participants were requested to avoid stepping into it) and virtual (a virtual planar obstacle was displayed on the screen of a liquid crystal display monitor). Trunk and feet kinematics were monitored, as well as electromyography (EMG) activity of 14 muscles of both lower limbs and trunk. The results of this study showed that the dominant choice for each obstacle investigated was not different between the real and virtual conditions. In addition, dynamic stability, economy and forward progression determinants guiding alternate foot placement were similarly satisfied. Thus the use of virtual planar obstacle in adaptive locomotion study is appropriate. EMG data were used to compute an index relating the changes in muscle activity relative to the normal walking profile. This EMG index was significantly and positively correlated with the amount of foot displacement for the adaptive step. The fact that the dominant choice resulted in minimum foot displacement from its normal landing spot combined with minimal changes in muscle activity validates conclusively the economy determinant.