## 4 Discussion  
This study aimed to verify the existence of interconnections between contralateral imbalances of the torque ratios of quadriceps and hamstrings and the three-dimensional positioning of the hemi-pelvises. As a matter of fact, our results support this assumption because a significant difference of the calculated crossed torque ratio was found between the two groups with a lower and higher pelvic torsion angle. The biomechanics of the pelvic bones and their joints is complex and has come into scientific focus over the past few years. Very low amplitude movements occur in the sacroiliac joints and the public symphysis, which could be the cause for complaints [1,25]. If we assume, in a simplified biomechanical model, that both hemi-pelvises are slightly twistable against each other ('inflare' [26,27]), three different cases can arise:  
1. The torque ratios are balanced both anterior-posterior and left-right (Figure 5a). Both hemi-pelvises are not tilted toward each other. 2. The absolute anterior and posterior torques are left-right different, but show the same ratio, with the torque of the knee extensors (more precisely, the torque of the rect  
Figure 4: Regression of crossed torque ratio and pelvic torsion angle (**above**) and of pelvic torsion angle and tenderness on palpation (**below**). \begin{table}
\begin{tabular}{c c} \hline
**Parameter** & **r** \\ \hline IPSI Flex & 0.218 \\ IPSI Ex & 0.476 \\ IPSI Ex/Flex & 0.472 \\ CON Flex & 0.262 \\ Con Ex & 0.203 \\ CON Ex/Flex & \textless{}0.001 \\ CTR (crossed torque ratio) & 0.668 \\ \hline \end{tabular}
\end{table} 
Table 3: Correlations (Pearson’s r) between the torque parameters and the pelvic torsion angle. quadriceps femoris) being predominant. This can lead to an anteversion of the pelvis, which affects both hemi-pelvises equally (Figure 5b). Shearing forces would not develop in the pubic symphysis. The influence of the relevant muscle groups on the positioning of the pelvis has been analyzed in other studies [14]. 3. The anterior-posterior torque ratios differ. If this is the case, the pelvis tilts forward on the side with the higher quadriceps-hamstrings ratio. The pubic symphysis may experience shearing forces (Figure 5c). The crossed torque ratio had the most expressed influence on the pelvic torsion angle. This is interesting because this harmonizes with our model-based assumption, according to which differing agonist/antagonist torque ratios between the left and right side are more decisive for torsion than the absolute values of the agonist-antagonist ratios. Differences in the agonist-antagonist torque ratios would, if they were identical left and right, allow the pelvis to antevert, but they would not necessarily have an effect on the torsion of the hemi-pelvises. The absolute torque of the muscles involved, however, do play a role, as shown by the correlation coefficient of the quadriceps at the side of the anteverted hemi-pelvis (quadriceps torque IPSI Ex, Table 3). The crossed torque ratio (Equation (3)) seems to have a more expressed influence, though. Nevertheless, our results do not allow a direct derivation of a causal connection. This means that we cannot identify the muscular torque ratios measured as a reason for the three-dimensional torsion of the hemi-pelvises and the increased tenderness to palpation in the pubic symphysis. However, the findings still fit in the pelvis movement model described. Only a few studies focus on the three-dimensional movement of the hemi-pelvises against each other and the sacrum. [PERSON] et al. describe physiological, rotatory movements of one degree in the pubic symphysis [28]. Strain caused by standing on one leg results in relative vertical shearing stress and tensile stress on the stabilizing sacroiliac joints, as well as in vertical shearing and pressure strain on the pubic symphysis [29; 25].