**3. Results**

Among the 20 subjects, the SNR resulted above the minimum selected value of 10 was in: (i) 5 subjects for both muscles of both legs, (ii) 8 subjects for both muscles of at least for one leg, (iii) 16 subjects for GM and 13 for TA for at least one leg. Therefore, a median of 159 (minimum 48, maximum 208) strides were considered per leg and per subject. For each subject, muscles that showed SNR greater than 10 and considered strides was reported in Table 1.


**Table 1.** For each subject, the muscles that showed a signal-to-noise ratio (SNR) larger than 10 are indicated with a cross. The number of strides considered per leg are reported in the bottom line.

*Analyzing gait symmetry:* no statistical di fference was found between the stride time data series of the left and right leg among subjects (maximum di fference for 25th percentile, median and 75th percentile between left and right side for each subject, 0,01 s). Since kinematic symmetry (i.e., stride time) was verified for all subjects, data from left and right leg together were analyzed to calculate n-activation pattern occurrence frequency and timing per subject and per muscle.

For GM, the most frequent (42.9 ± 0.8% occurrence frequency) was the 2-activation pattern: the first activation for all patients at the transition between flat foot contact and push-o ff; the second activation in 9 out of 16 subjects (1, 3, 6, 8, 12, 13, 14, 16, 19) at the turn of pre- and initial swing, in 2 (17 and 18) during terminal stance, in 1 (4) at initial swing, and in 4 (2, 10, 15, 20) during mid-swing.

The second most frequent (28.0 ± 1.0%) was 1-activation pattern, with a timing similar to the 2-activation pattern for all patients but with no activation during the swing phase.

The third most frequent (21.0 ± 0.9%) was the 3-activation pattern: the first two activations during stance in all subjects but with the exception of 3 (2, 10, 15), around stance-swing transition, in the first half, and at the beginning of swing, respectively; the third during initial and mid-swing for all subjects but 4 (2, 3, 4, 10) during final swing.

The fourth most frequent (7.5 ± 0.6%) was the 4-activation pattern: with an activation scheme similar to the 3-activation pattern during the stance phase and a high variability of the timing of very short activations during the swing phase.

The least frequent (2.5 ± 0.4%) was the 5-activation pattern that, with respect to the other patterns described above, showed several discontinuous activations with high variability during both stance and swing phases, with in some cases (1, 2, 14, and 19) a prolonged activation during mid-stance together with shorter ones.

Occurrence frequency of GM activation pattern is depicted in Figure 1, and timing over gait cycle of the 5 activation patterns for GM in Figure 2.

**Figure 1.** Occurrence frequency (mean ± SD) of the 5 activation patterns of gastrocnemius medialis (GM) over the 16 subjects for whom GM signal-to-noise ratio resulted above the selected threshold of 10.

For TA, the most frequent (39.5 ± 0.7%) was the 3-activation pattern: in 8 subjects out of 13 (1, 3, 6, 11, 15, 16, 17, 18) the first activation at the beginning, and in 5 (5, 8, 9, 12, 20) during mid/final stance; the second in the first half of the swing phase in 6 (3, 5, 6, 8, 15, 18, 20), around the stance to swing-transition in 5 (1, 9, 11, 12, 17), only in 1 subject (16) in the second half of the stance phase; the third in terminal swing for all subjects but 1 (16), anticipating the activation to initial swing phase.

The second most frequent (28.7 ± 0.9%) was the 4-activation pattern: the first at the beginning of stance for all subjects but 1 (20) at mid-stance; the second from mid- to final stance in 9 subjects (1, 3, 6, 9, 11, 12, 16, 17, 18), in 2 (15, 20) around stance to swing transition, and in 2 (5, 8) at the beginning of swing; the third in 5 subjects (5, 6, 15, 18, 20) at mid-swing, in 4 (1, 11, 16, 17) around stance to swing transition, and in 4 (3, 8, 9, 12) in the first half of swing; the fourth at the end of swing in all subjects but 1 (16) at mid-swing.

**Figure 2.** Mean ± SD activation intervals in percentage of gait cycle for 1- (**a**), 2- (**b**), 3- (**c**), 4- (**d**) and 5- (**e**) activation pattern in GM. Mean value of foot-off in percentage of gait cycle is represented with a red star, representing the beginning of swing phase.

The third most frequent (17.9 ± 1.0%) was the 2-activation pattern: the first in 5 subjects (1, 9, 11, 12, 18) during the second half of stance, in 4 (3, 5, 8, 17) around stand to swing transition, in 2 (6, 16) during the first half pf stance, in 1 (15) at midstance, and in 1 (20) during the first half of the swing phase; the between mid- or final swing for all subjects but 2 (6, 16) during initial swing.

The fourth (9.8 ± 0.6%) was the 5-activation pattern: first activation at the beginning of stance for all subjects; second variably distributed from initial to late stance in all subjects; third in 6 subjects (1, 9, 11, 12, 16, 17) in the second half of stance, in 2 (3, 8) at the stance to swing transition, in 5 (5, 6, 15, 18, 20) at the beginning of swing; the fourth between initial and mid-swing for all subjects but 2 around stance to swing transition (1) and in late swing (6); the fifth at the end of swing in 10 subjects (1, 3, 6, 8, 9, 11, 15, 17, 18, 20), at mid-swing in 2 (5, 16), and at early swing in 1 (12).

The least frequent (3.0 ± 0.4%) was the 1-activation pattern, exhibited only by 6 out of 13 subjects (1, 3, 5, 9, 12, 18), varying largely between the end of stance and the end of swing.

Occurrence frequency of TA activation pattern is depicted in Figure 3, and timing over gait cycle of the five activation patterns for TA in Figure 4.

**Figure 3.** Occurrence frequency (mean ± SD) of the 5 activation patterns of tibialis anterior (TA) over the 13 subjects for whom TA signal-to-noise ratio resulted above the selected threshold of 10.

**Figure 4.** Mean ± SD activation intervals in percentage of gait cycle for 1- (**a**), 2- (**b**), 3- (**c**), 4- (**d**), and 5- (**e**) activation pattern in TA. Mean value of foot-off in percentage of gait cycle is represented with a red star, representing the beginning of swing phase.

All GM n-activation patterns showed TA coactivation, for TA 2-, 3-, 4-activation patterns, at the beginning of stance from foot contact, approximately from 0% to 20% of the gait cycle, and in preparation of foot <sup>o</sup>ff, approximately from 55% to 65% of the gait cycle. With more than 1 GM activation (i.e., 2, 3, 4-activation patterns) a third TA coactivation phase was identified from mid-swing to foot contact again, approximately from 75% to 100% of the gait cycle.

Coactivation for TA 1-activation and 5-activation patterns was not reported due to rare occurrence of the former and large variability of intermediate activations in the latter.

Normalized n-activation patterns of GM and TA and corresponding coactivation intervals are depicted in Figure 5.

**Figure 5.** Normalized activation intervals of TA detected strides where GM (thicker lines) showed 1- (**a**), 2- (**b**), 3- (**c**) and 4- (**d**) activation pattern. Co-contractions intervals, where both concurrent patterns are above 0.1, are highlighted by vertical grey bands.
