**3. Results**

A summary of the experimental data is presented in Figure 3; the scatterplot of the regularity index vs. period index clearly shows the clusters related to speed and strategy, while the data concerning the four different sensors are partially overlapped. The non-normal distributions of RI values are made apparent by the ceiling effect toward the unitary value.

**Figure 3.** Summary scatterplot of all experimental outcomes: the period index is reported on the *X*-axis and the regularity index is reported on the *Y*-axis. Data from the four sensors are reported in separate plots. Different markers/color coding (refer to embedded legend) identify trial conditions (W1, W2, and W3 are for walking at 1.0, 1.4, and 1.8 m/s, respectively; R3 and R4 are for running at 1.8 and 2.2 m/s, respectively). The regularity index evidences an apparent ceiling effect.
