## 1 Introduction  
Despite the important number of patients affected every year (A World Health Organization report estimates the lifetime prevalence of non-specific low back pain (LBP) at 60 to 70% in industrialized countries [1]), few authors have investigated the mechanisms of the action of lumbar belts. These devices are part of a large series of care strategies for LBP and several clinical trials showed their clinical efficacy [2, 3]. However, their mechanical effects remain unclear and, consequently, it is almost impossible to propose an optimized belt design. Many studies found in the literature dealt with braces for scoliosis correction. [PERSON] et al. [4] proposed a link between brace wearing, interface pressure, and spine correction using the posture changes as a landmark. [PERSON] et al. measured the local intervertebral disk geometry with a low-dose radiation X-ray [5] or fluoroscopy [6] while wearing a belt, which demonstrated and quantified the spine posture changes induced by the medical device. [PERSON] et al. [2] studied the efficacy of lumbar belts by assessing the improvement of functional capacity, pain reduction, and drug consumption of 197 patients over 90 days. Two randomized groups were formed: one group wore the belt (Lombacross(r) Activity, Thuasne, France) and the other one was the control group. Both groups were allowedto use medication to help reduce pain. Three check-ups for each patient were done: the first one on the day of inclusion in the study, the second after 30 days, and the last after 90 days. Functional capacity was assessed by the EIFEL score, pain intensity was measured by a visual analogical scale, and medical consumption was counted as the number of days the patients were taking pain killers (analgesics, NSAID, and/or myorelaxants). The cost of care for these patients was also evaluated [7]. The cost per patient with a lumbar belt for 3 months was lower than that for the other group (\(\Delta\) = 205.726). This study shows that the group wearing a lumbar belt had a significant improvement of functional capacity, a significant reduction of pain intensity, and a significant reduction in medication consumption compared to the control group. [PERSON] et al. [8] also conducted a survey about the efficacy of lumbar belts on 108 patients that used a lumbar belt for more than 30 days. It included people suffering from LBP for more than 6 months. They did not have any criteria regarding age, sex, associated pathology, or context of pain. The lumbar belts used were Lombacross(r) (Thuasne, France), Lombax(r) (Thuasne, France), and Lombacross(r) Activity (Thuasne, France) or others (11%). The belts were worn for 1 month up to more than a year and were used daily (50%), often (32%), or occasionally (18%). The results are that 92% of the patients considered the belt to have good or very good efficiency; though there were some reports of discomforts (heat, bloating, difficulty to seat), 77% of the patients had a good tolerance. The way lumbar belts reduce pain is not well-known. Studies were conducted to better determine the effect of the belt on patients. Lumbar belts might reduce lumbar motion and, therefore, decrease the load on some vertebas and keep the body out of any harmful position. Moreover, the friction of the belt on the skin can also activate cutaneous mechanoreceptors, improve lumbar proprioception, and restore lumbar stability. [PERSON] et al. [9] studied the proprioception issues in patients suffering from LBP. They conducted a study that included 60 patients distributed into two groups: 38 patients in the LBP group and 19 patients in the control group. Patients from the LBP group answered a questionnaire (Roland Morris Disability Questionnaire) in order to evaluate their level of pain. Their lumbar instability was evaluated in 2 ways: a prone instability test (Prone IT) and a questionnaire based on 15 clinical signs of lumbar instability. There were three experimental conditions: no belt, extensible belt, and non-extensible belt.