## 2 Materials and Methods
### Musular Electrical Activity
#### 2.4.1 Musular Strength  
Regarding the muscular strength data, they should be collected using the force sensor instrument by pushing the force sensor device, which was fixed on the wall, in all sagittal plane movements of all lower limb joints, as much as possible. The collection of three trials for each muscle group was the main aspect of muscle strength data collection. During each trial, the foot pushes with a reset to zero in between was the basic step to collect the data properly. Given that the muscular strength measured by the force sensor has been validated [17], it must be pointed out that all body segments, including upper and lower extremities, may participate in the measured movement and cause some reading interference.  
To illustrate this, the method of measurement for muscular strength has been clarified in the following steps [19]:  
1. To measure the hip muscle strength, the participant was required to be in a comfortable standing position on a wooden step, and then to
* Push the force sensor device by the toes of their dominant leg forward and upward (standing while trying to keep the lower limbs as straight as possible while the force sensor was in front of the participant) as much as they can with an extended knee to collect the strength data of the hip flexor muscle group (Figure 5A).
* Push the force sensor device backward and upward by the heel of the dominant leg (standing with extended hip and knee joints while the force sensor was behindthe participant) as much as they can with an extended knee to collect the strength data of the hip extensor muscle group (Figure 5B).
2. To measure the knee muscle strength, the participant was required to be in the sitting position on a chair that is put on a wooden step to keep the hip and knee in 90-degree flexion and to support the ankle on the step simultaneously. Then, the participant should try to * Push the force sensor device by the foot of the dominant leg forward and upward as much as they can while being in a sitting position, with the force sensor in front of the participant to collect the strength data of the knee extensor muscle group (Figure 6A).
* Push the force sensor device by the foot of the dominant leg backward and upward as much as they can while being in a sitting position, with the force sensor under the chair to collect the strength data of the knee flexor muscle group (Figure 6B).
3. To measure the ankle muscle strength, the participant was required to be in a comfortable or natural sitting position on a chair while keeping the hip and knee in 90-degree flexion and the ankle in the neutral position; the heel should be maintained on another higher wooden step (sitting while the force sensor is in front of the participant). Then, the participant tried to * Push the force sensor device by the forefoot or toes of the dominant leg upward to the maximum level of the participant's ability to collect the strength data of the ankle dorsiflexor muscle group (Figure 7A).
* Push the force sensor device by the forefoot or toe of the dominant leg downwards to the maximum level to collect the strength data of the ankle plantar flexor muscle group (ankle extensor muscle group) (Figure 7B).  
Figure 5: Measurement of the hip muscle strength. (**A**) Hip flexors (toe force). (**B**) Hip extensors (heel force).