## 1 Introduction
They concluded that there was no statistical difference in the variability of lumbar proprioception between the two groups. The LBP group had a worse proprioception than the control group, but the study showed \"no improvement in lumbar proprioception with use of a lumbar belt for patients with LBP or for healthy control\". They also couldn't identify sub-groups of patients with LBP for whom using a lumbar belt would be better than for the others. In the field of engineering, the link among the textile characteristics, the belt design, the pressure applied on the trunk, and its effect on the human body and, particularly, on the spine was poorly studied--but it was proposed that the main mechanical effect of the lumbar belt is the pressure applied on the trunk; this pressure is supposed to force the patient to change his or her lumbar spinal posture (lordosis) by acting on the abdomen. [PERSON] et al. [10] proposed a clinical study using optical methods and pressure map sensors, but the method is tedious and time consuming, and some early-stage information would be of great help for the design of new belts. Some studies were conducted in order to identify parameters related to the performance of lumbar belts for patients. Another way of reducing pain is related to the change in posture. In the intervertebral disk, most of nerve endings are located in the posterior part, so even if many other reasons for the pain should be invoked [11], decompressing the back part of the disk could reasonably be associated with pain relief [12]. [PERSON] et al. [5] proposed a complete methodology to estimate and optimize the pressure distribution of the disks in the lumbar region. A bi-planar X-ray imaging system (EOS) giving the disk shape variations was associated to a Finite Elements Model of the disc and an optimization loop on the lumbar belt design. This methodology was proven to be efficient for restoring the lumbar curvature, but it is still impossible to understand the mode of action of the belt exactly and to separate purely mechanical effects and antalgic effects related to proprioception or to heat. In reality, the belt is acting on the skin, outside the body, and the medical effect is deep inside the body in the spine. Some recent research works are oriented to compare extensible lumbar belts with non-extensible ones for trunk postural balance in a static state or for sit-to-stand movement [13; 14]. In particular, [PERSON] et al. [15] and [PERSON] et al. [16] attempted to reveal the effect of lumbar belts on trunk muscle activity and lumbar stiffness. The way the load is transmitted was studied by [PERSON] et al. [17] in a numerical parametric study. They modelled the effect of three lumbar belts on four idealized numerical trunks of different morphologies: tall and thin, tall and large, small and thin, and small and large. Other factors were included in the study, such as the initial lordosis angle, the height of the subject, or the patient's soft tissues behavior. The results of this parametric study showed that the choice of the belt and the patient's morphology are governing factors in disk decompression. Surprisingly, the mechanical characteristics of the body structures have very little influence on the therapeutic treatment, except for the mechanical properties of intervertebral discs. Unfortunately, this first model only considered the global disk decompression but not the pressure variation inside a disk or other factors that should be related to the wearability and comfort. Moreover, the quality of the belt geometrical representation was poor, considering that the choice of the belt is influential. Recently, a semi-analytical approach based on real trunk shape and a more detailed belt structure has been proposed [18]. This approach provided a first in-silico pre-clinical trial that clearly outlines the influence of morphology on belt response; it also shows that the belt structure could change the treatment efficiency.