# System for Evaluation and Compensation of Leg Length Discrepancy for Human Body Balancing
## 5. Mechatronic System Design
### Experimental Results  
#### 5.4.1 Experiment 1: Healthy Population--Left and Right Leg Load Distribution  
The first experiment's goal was to test the new mechatronic system on the healthy population and to confirm the findings in [1], where it was concluded that people without LLD can also have asymmetrically distributed loads on their left and right legs. The experiment included 46 volunteers (23 women + 23 men). The study was conducted in accordance with the Declaration of Helsinki, and the protocol was approved by the Ethics Committee of the Bielovar University of Applied Sciences. The average volunteer age was 22.18 years (SD = 5.52 years). The criteria for exclusion from this group of volunteers were having LLD, scoliosis, incorrect posture, diabetes and Body Mass Index (BMI) > 30 [1]. In the first experiment, the volunteers' loads on their left and right legs were measured, as well as the position of the CoM (\(CoM_{x}\)). Under the researchers' supervision, the volunteers placed their left and right feet on specifically marked locations on the force plates. The distance between the volunteers' heels was 24 cm. The left and right force plates were set to the same height of 424.4 mm. The researcher gave the volunteers the instruction to maintain a naturally upright posture and to face forward. For every volunteer, the loads on their left and right legs were measured and the CoM along the \(x\)-axis (\(CoM_{x}\)) was found. This was done in 10 s with the application shown in Figure 17. With the help of a tailor's tape measure, the heights of the volunteers' LASIS and RASIS anatomical points were measured as compared to the basis. The BMI was calculated as the ratio of mass and squared height of the human body. The mean value, standard deviation and minimum and maximum of the conducted measurements are shown in Table 3. According to statistical results in Table 3, there is an asymmetry in the load on the left and right legs of healthy volunteers, which coincides with the research findings in [1]. Load measurements of the left and right legs and the CoM along the \(x\)-axis (\(CoM_{x}\)) for three chosen volunteers are shown in Figure 18 and Table 4. Volunteer 1 has a higher load on the right leg (Figure 18a) and a shift in the CoM along the \(x\)-axis higher than 0 (Figure 18b). Volunteer 2 has a higher load on the left leg (Figure 18c) and a shift in the CoM along the \(x\)-axis lower than 0 (Figure 18d). Volunteer 3 has approximately the same load on both the left and right legs (Figure 18e) and a shift in the CoM along the \(x\)-axis approximately equal to 0 (Figure 18f). The standard deviation of the \(CoM_{x}\) variable according to Table 4 is lower than 1 mm for all volunteers, pointing to a static posture. This confirmed the presumption that the projection of the human body's CoM in the transverse plane lies in the same point as the CoP [28]. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \multirow{2}{*}{**Variable**} & \multirow{2}{*}{\(CoM_{x}\)} & **Mass** & \(m_{L}\) & \(m_{R}\) & **Height** & **LASIS** & **RASIS** & **BMI** \\  & & [kg] & [\%] & [\%] & [\%] & [cm] & [cm] & [cm] & [kg m\({}^{-2}\)] \\ \hline Mean & \(-2.99\) & 75.26 & 51.12 & 48.88 & 174.9 & 101.2 & 101.2 & 24.45 \\ SD & 8.45 & 14.15 & 2.95 & 2.95 & 10.6 & 7.1 & 7.1 & 2.89 \\ Min & \(-27.08\) & 53.68 & 44.90 & 41.94 & 155.0 & 88.0 & 88.0 & 18.72 \\ Max & 15.38 & 108.92 & 58.06 & 55.10 & 193.0 & 115.0 & 115.0 & 29.76 \\ \hline \end{tabular}
\end{table} 
Table 3: Experiment 1: Measurement results of the CoM along the \(x\)-axis (\(CoM_{x}\)), mass, loads on the left (\(m_{L}\)) and right (\(m_{R}\)) legs, the positions of the LASIS and RASIS anatomical points, and the BMI. The loads on the left and right legs are shown as percentages [%] of the human body mass. Volunteers 1 and 2, although they are not diagnosed with LLD, have an asymmetrical load distribution on the left and right legs.