## 4 Discussion
### Test Persons with Low Back Pain  
The results in Table 4 show a difference in the mean values of both genders for different degrees of pain. This difference was investigated using ANOVA. The results show that there is a difference between the pain levels. The determination of the effect size (Table 5) shows at partial.etasq = 0.018 and omegasq = 0.016. A key disadvantage of the partial eta square is that it always overestimates the resolved variance. The distortion becomes smaller the larger the sample size becomes. For small samples, omega-square should be preferred as a measure of variance elucidation [47]. With a value of 0.016 it can be assumed according to [PERSON] that a small effect is present [48]. Furthermore, if the power is 0.87, it can be assumed that the false null hypothesis was correctly rejected and that the effect actually exists. The results show that test persons who give a Korff value (4 or higher) for back pain have a lower power conversion in the spectrum. This allows the conclusion that pain patients have lower vibration amplitudes and stand more rigidly. From the literature it is known that back pain often occurs in top athletes and people with poorly trained back muscles [49]. In scientific discourse, the connection between structural changes in the spinal column and back pain has not been clarified to date. In addition to functional diagnostics, imaging procedures such as magnetic resonance tomography are also used in diagnostics [50]. Another component in diagnostics is the measurement of postural control. Here it is true that back pain subjects have a reduced postural control [51]. Electromyography analyses of the trunk musculature revealed differences between people with back pain and healthy people [52; 53]. Increased latencies or a reduced level of muscular activity on a disturbance stimulus were found here [54; 52]. A further approach in diagnostics can be the consideration of the frequency spectrum of the posturographic measurement. The results showed that the spectrum of subjects with back pain differed from those without back pain (see Table 4). Comparing the spectrum of the back pain group with the spectrum of a double inverted pendulum according to [15], which was excited in the upper segment with 8000 N, a similar course is obtained (see Figure 7). The power conversion in the spectrum of the group of test persons compared to the model is negligible for the consideration, since the model represents an idealization of the measurement condition, as well as a strong simplification of the test person, and experiences a unique extrinsic excitation. However, the characteristic maxima between 0 and 0.6 Hz, and at 1.6 Hz, are also present in the model (see Figure 9). \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline  & **Test** & \(\boldsymbol{p}\) **Value** & **Etasq** & **Partial.Etasq** & **Partial.Omegasq** & **Power** \\ \hline Gender & 0.664 & 0.416 & 0.001 & 0.001 & \(-\)0.001 & 0.129 \\ Degree of Pain & 9.733 & 0.002 & 0.018 & 0.018 & 0.016 & 0.877 \\ Gender: Degree of Pain & 0.193 & 0.660 & 0.000 & 0.000 & \(-\)0.001 & 0.072 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Result of the ANOVA of the two observation groups Men/women with and without pain. The controlled models presented here also show comparable characteristics. Furthermore, the difference in the range of 0-1.5 Hz with 0.36 Nm\({}^{2}\) is similar to the difference of the male groups of Korff 1 vs. Korff \(>\) 4 (0.49 Nm\({}^{2}\)). This suggests that myosclerosis in the back, which often occurs in chronic unspecific back pain, causes the body to behave more like a double inverted pendulum than a triple inverted pendulum from a biomechanical point of view. This can be seen as a further indication that back pain subjects have a partial restriction in one degree of freedom. This also indicates that the regulation or neurological muscular control has an additional influence.