*2.2. Data Acquisition*

Each participant performed a 6-min walking test along a 15 m straight pathway at a self-selected speed wearing own comfortable footwear. Angular velocities of the shanks, used for gait temporal segmentation, were collected using two tri-axial synchronized inertial sensors (OPALs, Apdm, Portland, USA, sampling frequency = 128 Hz) attached to the lateral aspect of each ankle, approximately 0.05 m above the lateral malleolus, using elastic straps.

sEMG signals of GM and TA of both legs were acquired using wireless bipolar surface electromyograph, (Mini Wave, Cometa, Milan, Italy, sampling frequency = 2000 Hz). Sensor placement was performed following SENIAM guidelines [33]: for GM, the electrodes of the sensor were placed on the most prominent bulge of the muscle, aligned longitudinally along the leg [34]; for TA, at 1/3 along the line joining the head of the fibula and the tip of the medial malleolus [34]; bipolar sEMG electrodes are applied around the recommended sensor location with an inter electrode distance of 20 mm.

To synchronize the two systems, the accelerometers embedded in both sEMG sensors (Mini Wave, Cometa, Milan, Italy, sampling frequency = 2000 Hz) and inertial measurement units were used: before acquisition, one of the OPAL sensors was tapped three times on one of the Mini Wave sensor; synchronization was implemented during data processing matching the 3 acceleration peaks acquired by the two systems.
