The effect of functional inspiratory muscle training on diaphragm function and core stabilisation in patients with chronic non-specific low back pain: a randomised controlled trial

Chronic non-specific low back pain (CNSLBP) is associated with diaphragm-related core dysfunction and reduced dynamic spinal stability. This study investigates the effects of functional inspiratory muscle training (F-IMT) on diaphragm function, core endurance, respiratory muscle strength, and disability in individuals with CNSLBP. A randomised controlled trial was conducted with 40 patients with CNSLBP, randomly assigned to a multicomponent F-IMT-based rehabilitation group ( n = 20) or a thoracic expansion exercise (TEE) control group ( n = 20). Participants in both groups completed a structured 10-week training programme. The prespecified primary outcome was diaphragm thickness measured by ultrasonography at 10 weeks. Pain severity (Numeric Rating Scale), respiratory muscle strength (maximal inspiratory and expiratory pressure, MIP and MEP), diaphragm mobility, core endurance (McGill tests), and disability (Oswestry Disability Index, ODI) were secondary outcomes. After baseline adjustment, post-treatment diaphragm thickness was greater in the F-IMT group than in the control group (adjusted difference, 2.434 mm; 95% confidence interval [CI], 1.714 to 3.261; P < .001; partial eta-squared [ηp²] = 0.446). The F-IMT group also had lower pain and higher respiratory muscle strength, core endurance, and diaphragm mobility than the control group (all P ≤ .010). A significant group-by-baseline interaction was found for ODI ( P < .001; ηp²=0.249). The adjusted between-group difference favouring the intervention increased from 5.842 points at a low baseline ODI value to 15.130% points at a high baseline value. Compared with thoracic expansion exercises, the multicomponent F-IMT-based rehabilitation programme was associated with greater improvements in diaphragm thickness and mobility, pain, respiratory muscle strength, core stabilisation. These findings suggest that F-IMT may be a promising addition to a multi-component strategy for CNSLBP rehabilitation. ClinicalTrials.gov, NCT06958744, registered on 19/04/2025.