# Validation of a Wearable IMU System for Gait Analysis: Protocol and Application to a New System
## 2 Materials and Methods
### Experimental Setup for Validation
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Subject** & **Weight (kg)** & **Height (cm)** & **Age (years)** & **BMI** & **Gender** & **S\({}_{\text{anth}}\) (cm)** \\ \hline
1 & 58 & 168 & 31 & 20.5 & F & 59.5 \\
2 & 50 & 160 & 49 & 19.5 & F & 56.6 \\
3 & 62 & 164 & 19 & 23.1 & F & 50.9 \\
4 & 152 & 187 & 30 & 43.5 & M & 64 \\
5 & 70 & 169 & 32 & 24.5 & M & 57.8 \\
6 & 87 & 183 & 31 & 26.0 & M & 62.6 \\
7 & 46 & 154 & 29 & 19.4 & F & 54.5 \\
8 & 68 & 179 & 23 & 21.2 & M & 61.3 \\
9 & 78 & 178 & 29 & 24.6 & M & 60.9 \\
10 & 60 & 164 & 48 & 22.3 & F & 58 \\ average & 73.1 & 170.6 & 32.1 & 24.5 & 50\% & 59.1 \\ standard deviation & 30.3 & 10.7 & 9.5 & 7.0 & & 3.9 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Mean and standard deviation for personal data and parameters of the 10 subjects. \(S_{\text{anth}}\) = mean anthropometric step length. The measurements of reference GA kinematic are carried out by the Elite (BTS Milano, Italy) motion capture system in an eight-cameras setup at a 100 Hz sampling rate. Two dynamometric force platforms (Kistler, Winterthur, Switzerland) measured the ground reaction forces. The GA volume of interest is calibrated. _Subject setup_. Some anthropometric segments of the subject are measured: lower limb (ground-greater trochanter), ground-malleolus, lateral condyle-greater trochanter, malleolus-lateral condyle, and fifth metatarsal-malleolus. Width of the foot, length of the foot, and outer distance between the feet are acquired to the ground plane when the subject is resting in natural balance. Age, weight, height, and gender are collected for each subject too. Anthropometric measurement includes the shoes. These values are given as the input to the wearable kinematic model. Other anthropometric measurements are registered following the usual procedure of the clinical GA acquisition. According to the requirements that correspond to our biomechanical model for data processing and parameters computation, the wearable IMU should be placed close to the Center of Mass (COM). Usually, it is placed onto the pelvis, in a posterior central position, in correspondence with the sacrum bone. It is preferable to anterior positioning at the mid-point between the Superior Anterior Iliac Spines because artefacts due to abdominal breathing could be present. Passive retroreflective markers are placed on the body over the anatomical landmark of the subject. In our tests, this is carried out following the [PERSON] protocol setup [PERSON] (1954). Each subject is asked to walk over a linear path crossing the working volume of the optoelectronic system at a self-selected speed, as naturally as possible, and to introduce, before and after the walking phase, 5-s of standing to have the reference acceleration baseline (g = 1 along the vertical direction). Before starting the acquisitions, as training, the subject conducts some practice walking along the testing path to become familiar with it. When the subject feels himself/herself practiced with the environment and the setup, the test can start. _Measurement_. It is necessary to define the number of gait repetitions at a self-selected speed for each test session, because data are to be collected to verify inter-trial variability or repeatability validation. We define that each subject should execute at least three gait repetitions. When the  
Figure 2: A validation setup of the laboratory for the analysis of wearable IMUs (Inertial Measurement Units) for GA (Gait Analysis). The walking path is segmented into the region where only wearable IMUs provide data about the straight steps and the area in which both optoelectronic systems and wearable IMUSs are collecting the same data (GA analyzed stride). subject is pathological, three gait repetitions is a burdensome task and the fatigue may result in a modification of the test performance. It means that the values of the spatiotemporal parameters result in increased variability so that mean values and standard deviations will be abnormal.