Comparison between APAs and first step characteristics calculated with two different systems in Experiment I. A. Linear correlation between Peak ML, calculated from COP and trunk acceleration; B. Linear correlation between first step length, calculated from foot markers, and first step range of motion (RoM), calculated from the angular velocity; C. Bland-Altman plot comparing APA duration calculated from the COP and from the ACC. The central dotted line represents the mean difference between the devices, while the upper and lower lines represents the limits of agreement. CTR: control subjects, PD: subjects with Parkinson’s Disease (OFF).