# Study on the Minimum Operation Width of Human-Powered Bicycles for Safe and Comfortable Cycling
## 4 Results
### Minimum Operation Width Determination Based on Cycling Workload Threshold Analysis  
An Analysis of Variance (ANOVA) was conducted to assess whether there were statistically significant differences in the workload across the different operational widths and cycling speeds. The independent variable was the eight different operation widths and five speeds, respectively, and the dependent variable was \(\Delta HRV\) (calculated from _LF/HF_ using Function (1)). The results revealed a statistically significant difference in workload across both operational widths and cycling speeds (\(p<0.01\)).  
The diverse data types of \(\Delta HRV\) values and the designated operation width and speed underwent Classification and Regression Tree (CRT) analysis. This method, well-known for its capability to handle varied data types, was employed using SPSS 25.0 software to generate the decision tree, as shown in Figure 12. The analysis suggested that both factors significantly influenced \(\Delta HRV\) values, which reflect the cycling workload. As illustrated in Table 8, the operation width emerges as the most influential factor. This highlights the significant influence that both operation width and cycling speed exert on cycling workload. The standard error of 9.9, alongside an estimate of 150.6, indicates the reliability of the analysis.  
Figure 12 illustrates that within the specified width range of 0.65 m to 1.2 m, cycling workload tends to decrease as operational width increases, based on the analyses of Node 1 and Node 2. The division occurs at a speed of 19.25 km/h. For speeds at or below 19.25 km/h, the predicted change in heart rate variability (\(\Delta HRV\)) value is 3.497, which is below the cycling workload threshold of 19 (as indicated in Table 4). This suggests  
Figure 12: \(\Delta HRV\) classification tree based on width and speed.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Dependent Variable** & **Independent Variable** & **Importance** & **Normalized Importance** \\ \hline \(\Delta HRV\) & Operation Width (unit: m) & 24.601 & 92.0\% \\  & Speed (unit: km/h) & 26.739 & 100.0\% \\ \hline \hline \end{tabular}
\end{table}
Table 8: The importance of factors to \(\Delta HRV\) *.  
that cyclists remain within a safe and comfortable workload range. Conversely, at speeds exceeding 19.25 km/h, an operational width greater than 0.95 m is associated with reduced cyclist stress, as demonstrated by the threshold for Node 6. When the operational width is less than 0.95 m at speeds above 19.25 km/h, the cycling workload reaches the \"a little stressful\" level (\(\Delta HRV=22.5\), which exceeds the threshold of 19 for Node 5). Therefore, to ensure cyclist safety and comfort at speeds of 20 km/h or higher (rounded from over 19.25 km/h), an operational width of at least 1.0 m (rounded up from over 0.95 m) is essential.  
Additionally, within the range of the cyclists' speeds, the workload generally increases with speed, as illustrated by the data from Node 1, Node 2, Node 11, and Node 12. However, there is an exception for speeds below 4.4 km/h, as demonstrated by Node 7 and Node 8, where workload begins to increase as speed decreases. Furthermore, the threshold speed of 4.40 km/h marks a critical division in workload levels; below this speed, the cy-cling workload escalates to 26.707, entering the \"a little stressful\" range. Consequently, an operational width of 0.9 m (rounded up from over 0.85 m for Node 4) only meets the requirements for speeds of 10 km/h and 15 km/h.