Fig. 4

Changes in performance of the unpredictable partnered stepping task (PST) and associated interaction forces. a Changes in performance of the PST was quantified by the average whole-body spatial synchronization error between the leader and follower per trial. This was calculated as the mean value of the difference in the anterior-posterior position between the leader and follower with respect to the initial distance between them. The spatial synchronization error decreased from the first to last trial (i.e. performance improved) in the EE and NN dyads. However, this improvement in performance was only significant in the EE dyads (p < 0.05). b The improvements in spatial synchronization from the first to last trial of the unpredictable PST were not accompanied by changes in the range of interaction forces observed during those same trials