# Pilot Studies of Vibrations Induced in Perambulators When Moving on Different Surfaces
## 3 Results and Discussion
### Normative Evaluation  
Figure 7 shows examples of the vibration of the research subject in the time domain before and after normative frequency-weighting for comfort evaluation. A significant magnitude reduction can be observed for \(y\) and \(z\) (horizontal) directional components. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Symptoms from Organs and** & **Frequency Ranges** & **Frequency Ranges Where** \\
**Other Parts of the Human** & **Considered to Be Disruptive** & **Reactions Are** \\
**Body Subject to Vibration** & **[Hz]** & **Very Intense [Hz]** \\ \hline General wellbeing & \(1\div 20\) & \(4.5\div 9\) \\ \hline Dizziness & \(9\div 20\) & \(13\div 20\) \\ \hline Strong jaw vibrations & \(6\div 8\) & - \\ \hline Apnoea & - & \(1\div 3\) \\ \hline Breathing disorders & \(4\div 8\) & - \\ \hline Stomach ache & \(4\div 14\) & \(4.5\div 10\) \\ \hline Strong increase of muscle tone & \(10\div 20\) & \(13\div 20\) \\ \hline Chest pain & \(4\div 11\) & \(5\div 7\) \\ \hline Lumbo-sacral pain & \(6.5\div 20\) & \(8\div 12\) \\ \hline Urinary urgency & \(9\div 20\) & \(10\div 18\) \\ \hline Faecal urgency & \(9\div 20\) & \(10.5\div 16\) \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Examples of ranges of the resonance frequencies for subjective human reactions [33]. Figure 7: _Cont_. The frequency-weighted RMS acceleration values, calculated according to the aforementioned ISO methodology, are shown in Table 4 and Figure 8.  
According to the discomfort levels from ISO 2631-1:1997 [18] (Figure 8), all the vibrations whose vibration total values (\(\mathbf{a}_{w}\)) exceed 0.315 m/s\({}^{2}\) are not comfortable. Thus, \begin{table}
\begin{tabular}{c c c c c c c c c c c c c} \hline \hline  & & \multicolumn{3}{c}{**Modern Pram—Surface Variants**} & \multicolumn{5}{c}{**Old Pram—Surface Variants**} \\ \cline{2-13}  & **Model** & **Model** & **Model** & **Model** & **Model** & **Model** & **Model** & **Model** & **Model** & **Model** & **Model** & **Model** & **Model** & **Model** & **Model** \\ \hline \(a_{ww}\) & \(\left[\frac{\mathbf{m}}{\mathbf{s}^{2}}\right]\) (RMS) & 1.70 & 2.50 & 4.03 & 3.81 & 4.28 & 4.57 & 0.44 & 0.90 & 2.08 & 2.23 & 3.41 & 3.26 \\ \hline \(a_{wy}\) & \(\left[\frac{\mathbf{m}}{\mathbf{s}^{2}}\right]\) (RMS) & 0.36 & 0.22 & 0.81 & 0.72 & 1.08 & 1.09 & 0.23 & 0.20 & 0.51 & 0.53 & 0.85 & 0.97 \\ \hline \(a_{wz}\) & \(\left[\frac{\mathbf{m}}{\mathbf{s}^{2}}\right]\) (RMS) & 0.26 & 0.27 & 1.00 & 0.50 & 0.80 & 0.58 & 0.21 & 0.20 & 0.45 & 0.33 & 0.77 & 0.60 \\ \hline \(a_{w}\) & \(\left[\frac{\mathbf{m}}{\mathbf{s}^{2}}\right]\) (RMS) & 1.76 & 2.53 & 4.23 & 3.91 & 4.49 & 4.74 & 0.54 & 0.94 & 2.19 & 2.31 & 3.60 & 3.45 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Weighted RMS acceleration values (calculated in accordance with ISO 2631-1:1997 [18]) applied to the weight placed in the space provided for a child in the tested perambulators. Figure 8: Comparative bar graphs of the weighted RMS acceleration values from ISO 2631-1:1997 [18]. Figure 7: Comparison of vibration acceleration orthogonal components for dirt road (Figure 2d) between original (black) and frequency-weighted (purple) in both time and frequency domains. in agreement with the normative assessment, riding in each of the perambulators at a speed of 4 km/h would not be comfortable. However, on the smoothest surface, the asphalt road (Figure 2a), after changing from the modern pram to the old pram, the discomfort level decreases from \"very uncomfortable\" to between \"a little uncomfortable\" and \"fairy uncomfortable\". On the concrete paving blocks (b), the discomfort level for the modern perambulator was already \"extremely uncomfortable\" while for the old perambulator only between \"fairly uncomfortable\" and \"uncomfortable\". On more uneven surface combinations, concrete plates (c) and the dirt road (d), the discomfort level for the old pram was between \"very uncomfortable\" and \"extremely uncomfortable\".