*3.2. Signal Acquisition*

Signal acquisition was achieved by means of the multichannel recording system Step32 (Medical Technology, Italy, Version PCI-32 ch2.0.1. DV; resolution: 12 bit; sampling rate: 2 kHz). Volunteers were instrumented with one knee electrogoniometer, three foot-switches, and four sEMG probes for each leg. Experimental set-up is depicted in Figure 1. Then, they walked for around 5 minutes with bare feet at self-selected pace following an eight-shaped path, which includes natural deceleration, reversing, curve, and acceleration. Experiments were performed in the Motion Analysis Laboratory of Università Politecnica delle Marche, Ancona, Italy. An electro-goniometer (accuracy: 0.5◦) was applied to the lateral side of each leg for measuring knee-joint angle in the sagittal plane.

**Figure 1.** Experimental set-up. MH1 and MH5 are first and the fifth metatarsal heads, respectively. TA, tibialis anterior. GL, gastrocnemius lateralis. VL, vastus lateralis. MH, medial hamstrings.

Foot-switches were applied under the heel, the first and the fifth metatarsal heads of each foot for measuring foot–floor-contact signal. sEMG signals were registered by means of three single-di fferential probes with fixed geometry placed over tibialis anterior (TA), gastrocnemius lateralis (GL), and medial hamstrings (MH) and one further single-di fferential probe (minimum inter-electrode distance: 12 mm) with variable geometry placed over vastus lateralis (VL). Electrode location and orientation were carried out under the supervision of a skilled licensed physical therapist, complying with SENIAM recommendations [31]. sEMG signals are exactly the same collected for the previous study of the present group of researchers [14]. Characteristics of foot-switches are: size = 11 × 11 × 0.5 mm and activation force = 3 N. Foot-switch signals are used to identify stance/swing phases and HS and TO events considered as ground-truth.
