## 2 Materials and Methods
### Experimental Protocol  
Subjects were instructed to walk in a pathway eight meters long inside the Santa Corona hospital motion analysis lab (Pietra Ligure, Savona, Italy, see paragraph below). Each participant walked both with and without exoskeleton. In the latter case (normal walking, or NW), subjects were asked to walk barefoot, as naturally as possible, at their preferred speed. In the former case, subjects walked under five different assistive modalities: bilateral fixed assistance set to the maximum (100%, B-FA), no assistance (B-NA), bilateral adaptive assistance (B-AA), unilateral adaptive assistance provided either to the left or the right leg (U-AA, U-NA depending on the assistance or not assistance condition of the considered leg, respectively). The order of presentation of these walking modalities was randomized among subjects (see Figure 2).  
To initiate the steps, we used the pro-step mode, and therefore, the subjects were instructed, prior to the start of the experiment, to shift their weight forward and toward a side to trigger the beginning of a step with the contralateral foot. Before the experimental session, an experienced therapist adjusted the hip width as well as the length of the upper and lower leg of the exoskeleton according to the anthropometric characteristics of the subjects and set the gait parameters--step length, step height, and swing time--in order to match the individual natural walking patterns (see Table 2).  
For each subject, these parameters were not changed during the experiment, i.e., they were set at the same value for all the assistive modalities.  
Since subjects always use either crutches or a walker when walking with the Ekso, in this experiment, all the subjects were tested with both aids. Moreover, three subjects (S2, S7, and S8) were also evaluated when walking without an exoskeleton with both aids to exclude that the differences in the muscular activation patterns when walking with and without the exoskeleton were due to these aids.  
\begin{table}
\begin{tabular}{c c c c c} \hline  & **Subjects Height** & **Step Length** & **Step Height** & **Swing Time** \\  & **[cm]** & **[inches]** & **[inches]** & **[s]** \\ \hline
**S1** & 179 & 15.0 & 1 & 1.35 \\
**S2** & 175 & 14.5 & 1 & 1.30 \\
**S3** & 155 & 13.5 & 1 & 1.20 \\
**S4** & 183 & 15.5 & 1 & 1.40 \\
**S5** & 178 & 15.0 & 1 & 1.35 \\
**S6** & 182 & 15.5 & 1 & 1.40 \\
**S7** & 158 & 13.5 & 1 & 1.20 \\
**S8** & 184 & 15.5 & 1 & 1.40 \\ \hline \end{tabular}
\end{table}
Table 2: Gait parameters for the Ekso set for each subject.  
Figure 2: Experimental protocol.  
We had a familiarization phase of 30 min of walking with the Ekso in the different walking conditions outside the lab setting. Afterwards, in the lab settings, subjects walked 16 m (one time back and forth in the lab) in each condition before starting the recording. In order to avoid the effects of the acceleration and deceleration phases at the beginning and at the end of the walk pathway, we considered for the analysis only strides in the middle of the pathway i.e., the strides during steady walking.  
With this procedure, we collected a minimum of 10 strides for the normal walking condition and a minimum of 12 strides for the Ekso-based modalities; half of those started with the right leg, and half started with the left one.