The aim of this trial is to assess the effectiveness and cost-effectiveness of a supervised and more personalised mhealth intervention compared with conventional exercise therapy in people with chronic non-specific low back pain.

Background: Chronic non-specific low back pain (CNLBP) is a prevalent and costly condition that encourages research into self-management strategies. Mobile health (mhealth) applications are promising interventions, but current evidence on their effectiveness is still conflicting. The aim is to investigate the (cost-)effectiveness of a supervised and personalized mhealth intervention, compared with conventional exercise therapy in individuals with CNLBP. Methods: A multicentre trial-based economic evaluation was designed to compare a mhealth intervention with conventional exercise. Participants will be recruited from two physical therapy rehabilitation clinics located within the participating centres. Adults aged between 18 and 59 years and with self-reported LBP >12 weeks will be included. Following the collection of baseline data, participants will be randomly assigned to one of two groups using a permuted block randomization: 1) mhealth; 2) Conventional exercise delivered through a booklet. Outcome assessments will be conducted following randomisation at five distinct time points, resulting in a total follow-up period of 12 months. The primary clinical outcome is disability (Roland-Morris Disability Questionnaire), while secondary outcomes include pain (NRS), utility (EQ5D5L), fears and beliefs (FABQ), self-efficacy (PSEQ), and global perceived effect. A sample size of 146 participants was estimated (73 allocated to each group) in order to detect a 2-point between-groups difference on disability. A cost-effectiveness study will be conducted alongside the trial, comparing the two interventions in terms of costs and clinical outcomes. Discussion: While mhealth applications show promise as interventions for people with LBP, there is still a gap regarding the type of delivery and personalisation strategies. This study investigates whether the implementation of stratified and tailored care within a mobile application, based on patient-reported outcome measures and supervised by a physiotherapist, is (cost)effective.

Inclusion Criteria:

• Adults aged between 18 and 65 years;
• Self-reported low back pain for more than 12 consecutive weeks prior to the study, with pain intensity ≥4 in the numerical rating scale (NRS);
• Not having participated in physiotherapy sessions for treatment of low back pain for at least 6 months prior to the start of the study;
• Having a smartphone with internet access;
• Self-management activation classified as Level 2 or higher (i.e., classifications of low, medium and high knowledge about self-management), according to the Patient Activation Measure (PAM) questionnaire.

Exclusion Criteria:

• History of spinal trauma or fracture;
• Diagnosis of spinal osteoarthritis, fibromyalgia, or rheumatic diseases; 3) Referred pain (from viscera, appendicitis, abdominal and pelvic pain);
• Previous spinal surgery;
• Presence of red flags, signs and/or symptoms of neurological impairment;
• Pregnancy.

Blinding the therapists will not be possible due to the nature of the interventions. Because outcomes are self-reported, blinding participants to the intervention will also not be possible. However, an assessor who will be unaware of the group allocation will perform the data collection. The researcher responsible for the statistical analysis will also be blinded to the group allocation (i.e. they will receive the data sheet with the groups/individuals coded numerically).