## 2 Materials and Methods
### Simulation Test Matrix and Outputs  
The impact velocities tested in the MADYMO simulations (8, 10, and 12 m/s) were selected to match those used in the physical impact tests presented in Table 1. The simulation test matrix shown in Table 2 includes variations in posture (standing and jumping), impact position (left, middle, and right), and countermeasure design, resulting in a total of 216 simulations.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Foam EAC** & **3 mm ABS Shell** & **1 mm Aluminium Shell** \\ \hline
7.5 m/s & 7.5 m/s & 7.5 m/s \\
10 m/s & 10 m/s & 10 m/s \\
11.5 m/s & 11.5 m/s & 11.5 m/s \\ \hline \hline \end{tabular}
\end{table}
Table 1: Impact test matrix.  
Figure 7: Track-guard countermeasure design to be used in conjunction with FFG.  
Simulation outcomes were categorised as fatal, hospitalised, or survived. Fatal outcomes included the most severe contact events and AIS 6 head injury. Contact involving the head, torso, or third rail are grouped together and classified as fatal. These scenarios include severe outcomes such as decapitation or electrocution, and as such, subsequent metrics like HIC\({}_{15}\) score or limb contact are not considered. Simulations without these high-severity contact events are assessed further. HIC\({}_{15}\) is used to calculate the risk of AIS 6 and AIS 3+ head injury [19]. AIS6 head injuries are deemed unsurvivable and are categorized as fatalities [20]. Hospitalisation was determined by limb contact with the wheels or AIS 3 to AIS 5 head injury. Previous publications suggest that cases of amputation without other complications rarely lead to fatality. This two-tiered classification allows for a more meaningful interpretation of survivability and treatment severity across the different countermeasure configurations (See Figure 8).  
The notches in the resulting box plots represent an approximation of the 95% confidence interval for the median, calculated using an asymptotic normality approximation as described by [21] (Equation (1)). In this study, non-overlapping  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Countermeasure** & **Impact Posture** & **Impact Position** & **Impact Velocity (m/s)** & **Total** \\ \hline \multirow{4}{*}{Baseline} & Jumping (x2) & Jumping High (Left Middle Right) & 8 & \\  & Standing (x2) & Jumping Low (Left Middle Right) & 10 & 54 \\  & & Standing (Left Middle Right) & 12 & \\  & Jumping (x2) & Jumping High (Left Middle Right) & 8 & \\ Front Panels (FP) & Standing (x2) & Jumping Low (Left Middle Right) & 10 & 54 \\  & & Standing (Left Middle Right) & 12 & \\  & Jumping (x2) & Jumping High (Left Middle Right) & 8 & \\ Full Front Guard (FFG) & Standing (x2) & Jumping Low (Left Middle Right) & 10 & 54 \\  & & Standing (Left Middle Right) & 12 & \\  & Jumping (x2) & Jumping High (Left Middle Right) & 8 & \\  & Standing (x2) & Jumping Low (Left Middle Right) & 10 & 54 \\  & & Standing (Left Middle Right) & 12 & \\ \hline \hline \end{tabular}
\end{table}
Table 2: Countermeasure design simulation test sample (N = 216).  
Figure 8: Injury categorisation flow chart.  
as indicating a statistically significant difference in medians at approximately \(p=0.05\). This visual method was applied to compare simulation outputs across countermeasure configurations, including primary- and secondary-contact HIC\({}_{15}\) scores.  
\[Notch=Median\ \pm 1.57x\frac{IQR}{n^{0.5}} \tag{1}\]