BREATHE-(H)IT: Multimodal whole-body high-intensity training to improve inspiratory muscle function in persons with chronic nonspecific low back pain

Abstract

Low back pain is the leading cause of disability worldwide, affecting more than 600 million people, with the prevalence expected to exceed 800 million people by 2050. Although most low back pain cases are acute and self-limiting, a substantial proportion of individuals develop persistent symptoms. In the absence of a clear pathoanatomical cause, these symptoms are classified as chronic nonspecific low back pain (CNSLBP). The biopsychosocial model provides a useful framework to understand CNSLBP, acknowledging the interplay between biological, psychological, and social factors that contribute to pain intensity and levels of disability. Within this framework, there is increasing recognition of the need to identify modifiable underlying mechanisms that contribute to CNSLBP. Inspiratory muscle dysfunction has emerged as one such potential mechanism. Inspiratory muscle dysfunctions, including reduced inspiratory muscle strength, endurance, activation, or increased fatigue, may contribute to the development and persistence of low back pain. However, the magnitude and prevalence of these dysfunctions, and their associations with clinical characteristics such as pain, disability, or psychological factors, remain unclear. Moreover, assessment of inspiratory muscle function often relies on invasive and costly methods, such as transesophageal diaphragm electromyography (EMG). While these techniques provide specific and direct insights into diaphragm activity, they are technically complex and less suitable for repeated measurements in clinical or research settings. This underlines the need to explore whether non-invasive methods, such as surface EMG of extradiaphragmatic inspiratory muscles, could also serve as an alternative. In recent years, high-intensity training (HIT) has gained attention as a promising intervention in CNSLBP. Evidence suggests that HIT is feasible, well-tolerated, and more effective than moderate-intensity training (MIT) in improving key outcomes such as physical disability. Despite these promising findings, the underlying mechanisms through which HIT exerts its benefits remain poorly understood, limiting the ability to optimize exercise prescriptions and to communicate their rationale to patients and clinicians. As inspiratory muscle dysfunction has been identified as a potentially modifiable factor in CNSLBP, it may represent a mechanism through which HIT produces its therapeutic effects.