The study will evaluate the clinical efficacy and performance of the BTL-043 and BTL-899 devices for alleviating back pain. It is a prospective, multi-center, open-label, single-arm study. Subjects will be required to complete four (4) treatment visits and two (2) follow-up visits. At the baseline visit, the Oswestry Disability Index (ODI), Visual Analogue Scale for pain (VAS), the Quebec Back Pain Disability Index (QBPDS), palpation of the treatment area, Fingertip-to-Floor-Flexion (FTFF) test, and Lateral FTFF test will be performed. Additionally, two-dimensional (2D) photographs of the subject's posture from the left and right profile will be taken, their Fitzpatrick skin type assessed, and the subject's weight and height will be recorded. The treatment administration phase will consist of four (4) treatment visits, delivered 5-10 days apart. During each treatment visit, subjects will receive treatments with both study devices, BTL-043 and BTL-899, consecutively, one immediately after the other. Therapy time will be set to 30 minutes for each treatment with each study device. After the last treatment, the subjects will complete the ODI, QBPDS, the Therapy Comfort Questionnaire (TCQ), and the Subject Satisfaction Questionnaire & Quality of Life Questionnaire (SSQ & QoL), along with the VAS, undergo palpation of the treatment area, FTFF, Lateral FTFF, weight and height measurements, and 2D photographing. During the 1-month and 3-month follow-up visits, the subjects will complete the SSQ & QoL, the ODI, QBPDS, VAS, undergo palpation of the treatment area, FTFF, Lateral FTFF, weight and height measurements, and 2D photographing. Safety measures will include documentation of adverse events (AE), which will be assessed after each procedure and at all follow-up visits.