*2.2. Participants, Motor Tasks, and Raw Data*

Twenty-five healthy subjects (14 males and 11 females, age range of 20–40 years) were recruited for the experiment (see details in Table 1). They signed an informed consent under the approval of the local Ethics Committee.


**Table 1.** Participants' demographic and anthropometric data. M—male; F—female.

Sensors were attached, by their flat surface, to the following landmarks: posterior aspect of spinous process of the seventh cervical vertebra (C7), midpoint between posterior superior iliac spines (pelvis), on dorsal aspect of the right wrist (wrist), and on lateral aspect of right ankle (ankle) (see Figure 1). Sensors were positioned in order to align their *X*-axes with longitudinal/vertical anatomical axes, sensor *Z*-axes were perpendicular to the sensor flat surface and were oriented accordingly.

**Figure 1.** Subject equipped with four wearable triaxial accelerometers (Cometa Systems, Italy) positioned with elastic bands on the seventh cervical vertebra (C7), pelvis, wrist, and ankle. Sensor positions are circled in red, and axis directions are reported nearby.

The experiments were carried out on a treadmill and consisted of steady-state walking at 1.0, 1.4, and 1.8 m/s, and of steady-state running at 1.8 and 2.2 m/s (trials respectively labeled W1, W2, W3, R3, and R4). After taking between 30 and 60 s to reach steady-state locomotion, the duration of measurements was fixed at 70 s, the initial and final five seconds sections were discarded, and the further analysis was performed on the central one-minute-long recording. Trial sequences were randomly balanced among subjects; half of the participants performed the sequence W1, W2, W3, R3, and R4, and half performed the reversed sequence from R4 to W1.

Measured accelerometric components were low-pass filtered (fourth-order Butterworth filter, cutoff frequency 5 Hz, 0.5 dB of peak-to-peak ripple in pass-band, and 20 dB of attenuation in stop-band). Finally, acceleration module *a* was computed as the norm of the three measured orthogonal components (*ax, ay*, and *az*) according to the following formula:

$$a = \begin{vmatrix} \stackrel{\rightarrow}{a} \\ \end{vmatrix} = \sqrt{a\_x^2 + a\_y^2 + a\_z^2}. \tag{2}$$

The experimental dataset consisted of 500 recordings obtained from 25 subjects, each performing five tasks, and equipped with four sensors.
