# Biomechanical Task-Based Gait Analysis Suggests ReWalk Gait Resembles Crutch Gait
## 2 Materials and Methods
### Signal Processing  
A band-pass filter (4 th order Butterworth; 20 to 500 Hz) was applied to the _EMG_ data, then we obtained the envelope function, a common approach ([PERSON] et al., 2017; [PERSON] et al., 2018; [PERSON] et al., 2018) when comparing muscle activation levels, by calculating the waveform length (_WL_) ([PERSON] et al., 2018; [PERSON] et al., 2018). The merits of the _EMG WL_ reside in the fact that both amplitude and frequency are taken into account, as shown in Equation (1) below:  
\[EMG~{}WL(n)=\sum_{i=n-N+2}^{n}|EMG(i)-EMG(i-1)| \tag{1}\]  
where \(n\) is the current sample and \(N\) is the window size.  
The knee, hip, and ankle joint angles on the sagittal plane were also estimated so that changes due to different gait conditions could be evaluated. The IMU sensors used in this study provide 3D orientation data using information from the built-in acceleration, rotation, and earth magnetic field sensors. The joint angles were estimated by calculating  
Figure 1: Signal processing and representation of data acquired during gait sessions. (**a**) Gait event detection via acceleration (red lines) and angular velocity (blue lines) obtained from IMU sensors placed on the shank. The IMU data obtained from the shank of subject 1 is shown for each gait condition. The points at which the foot makes initial contact and leaves the ground are marked with black circles and red squares, respectively. (**b**) The top panel shows the EMG WL of soleus muscle during three gait cycles. Using the ipsilateral FC position (black lines), the SL EMG WL can be segmented into gait cycles (second panel). The blue, green, and red lines depict contralateral limb LO, contralateral limb FC, and ipsilateral limb LO, respectively. The third panel shows the ensemble-mean and SD of the SL EMG WL within a gait cycle with a black line and grey area, respectively. In addition, the red, green, and blue stages depict the WA, SS, and LA phases, respectively. The bottom panel depicts the mean SL EMG WL normalized against the respective phase progression.  
the relative orientation of the IMU sensors, on the sagittal plane, that reside on each side of the respective joint. For instance, the knee joint angle was calculated by subtracting the orientation of the tibia from that of the thigh [35]. Once the FC and LO events were identified, the signals were segmented into gait cycles. We then normalized the signals along the time axis for each gait cycle, and the data was further represented as ensemble averages and standard deviation (S.D.). The data was further divided into the three gait-related biomechanical phases: WA, SS, and LA [1]. The WA phase begins with the FC of the ipsilateral limb and lasts until the LO of the contralateral limb. The subsequent SS phase ends with the FC of the contralateral limb, followed by the LA phase, which lasts until termination of the gait cycle (Figure 1b). All data processing was performed using a custom-built MATLAB (Mathworks Inc, Natick, MA, USA) code, and Wilcoxon signed rank tests were performed to assert any statistical significance.