## 4 Discussion
### Influence of Lumbar Belts  
A lumbar belt can act on the body in three different ways: its global stiffness, its shape, or the component arrangement.  
The pressure being proportional to the tension, and given that the belt stretch is fixed, it should be directly proportional to the stiffness. Here, the results show a high correlation between mean pressure and stiffness (R\({}^{2}\) = 0.999). On the other hand, the correlation with the maximum pressure was low--quantified using the last quintile (R\({}^{2}\) = 0.328). The fabric-based belts have a pressure variation--and consequently a maximum pressure--twice that of the textile-band-based belts. This result remains valid for all the morphologies, except for the small-large morphology, where the belt design has almost no influence on the pressure peak. This last situation can be explained by a change in the localization of the highest pressures: for thin subjects, the pressure peak is located on the two sides; for the fat ones, this maximum moves to the abdomen, with a shape ratio giving more pressure variations for the small/fat subject. Even if no clinical proof can support this assumption already, we can imagine that the maximum pressure has an incidence on the belt's comfort and possibletrouble, thus the patient compliance should be better with textile-band-based belts. It is much more difficult to conclude on the design parameters' influence on the lordosis angle.  
The design parameters and the global stiffness are correlated, but a multivariate analysis is not powerful enough to give a result. Indeed, this outlines the importance of body shape on the pressure generation first, and, secondly, on the lordosis angle variation.  
As a partial conclusion, the design parameter (fabric-based or band-based) has a significant influence on the comfort (using maximum pressure index), but not on the postural efficiency (using the lordosis angle index).  
As explained earlier, it is possible to assume that the pressure peak ratio is related to the wearability and that the lordosis angle variation is related to the efficiency. Figure 7 presents a way to classify the belts according to these two main directions. In order to achieve a presentation as independent of body shape as possible, a relative efficiency is obtained by dividing the angle variation by the mean value of each case.  
Therefore, efficient belts should have the following characteristics:  
* A max/mean pressure index as small as possible
* A relative angular variation as big as possible
* An area as small as possible, meaning that the belt has a behavior as independent as possible of the patient's morphology.  
Using these criteria, belts A, B, C, and D (all band-based design) have a rather limited efficiency, but with a very good wearability and a high adaptability to the patient's morphology. E, F, and G have a more unstable behavior, all having a higher-pressure peak ratio.  
Figure 7: Belt representation with the efficiency index (Relative angular variation) as function of wearability index (Max/Mean pressure ratio) for the four patient morphologies.  
Finally, belt E should be considered as a good choice, its efficacy being significantly higher than the others while keeping a good wearability index.