*3.3. Regularity Index: Effect of Locomotion Speed*

The effect of speed on regularity was highlighted by the comparisons between trials with the same locomotor strategy and with contiguous speeds (see Figure 4C). The tested couples were W1 vs. W2, W2 vs. W3, and R3 vs. R4. Regularity during walking trials significantly increased with increasing velocity, getting very close to the unit value for higher speeds. On the contrary, increasing velocity in running did not increase regularity. Nonetheless, it has to be noted that all values related to running showed a tendency to a ceiling effect with regularity indexes, limited in their values by the unitary upper limit, which marks a perfect regularity.
