Low back pain is the number one cause of disability worldwide with important socio-economic implications. In Belgium, 7 out of 10 persons will suffer from low back pain during their life, and 29% of all sick leave days are due to it. Chronic low back pain is defined as persistent pain for a period of minimal 12 weeks. In 85-90% of the CLBP cases, the pain cannot be attributed to a definitive underlying pathoanatomical cause, and is therefore labelled as chronic nonspecific low back pain (CNSLBP).~International guidelines recommend exercise therapy as the first-choice treatment for CNSLBP. A crucial factor within this context is exercise intensity. Indeed, multimodal high intensity training (HIT) leads to higher improvements in disability and cardiorespiratory fitness compared to moderate intensity training (MIT) in persons with CNSLBP. However, the underlying mechanisms for the additional value of a HIT approach remain largely unknown. Interestingly, low back pain is associated with impairments in diaphragm function, as the diaphragm is not only a principal inspiratory muscle, but also plays an essential role in postural control. The latter is a key factor in the development and maintenance of CNSLBP.~In this randomized controlled trial, 64 persons with CNSLBP will be recruited through local distribution of flyers and adverts on social media. The sample size calculation is based on (1) the therapeutic effects of a 12-week HIT program (compared to a MIT program) on the maximal oxygen uptake (VO2max) in persons with CNSLBP and (2) the therapeutic effects of a 8-week high-intensity inspiratory muscle training program (compared to a low-intensity inspiratory muscle training program) on the maximal inspiratory pressure (MIP) in persons with CNSLBP. These outcomes were chosen as they relate to the respiratory system and are thus most fitting to indicate possible effects on diaphragm functioning. The sample size calculation is based on the requirement of a minimal clinically important difference of 3-3.5ml/kg/min (VO2max) and 17.2 H2O (MIP). The power calculation resulted in a total of 63 persons. Therefore, the investigators plan to recruit 64 patients.~Participants will be randomly assigned to a HIT program or a MIT program. Primary outcomes are diaphragm muscle strength, -endurance, -fatigue and - activation. Secondary outcomes are cardiorespiratory fitness, postural control, pain, disability, depressive mood and anxiety. Primary and secondary outcomes will be assessed at 5 timepoints (0 weeks, 6 weeks, 12 weeks, 3 months after intervention, 12 months after intervention).~To analyze the data, JMP Pro (15.2 SAS Institute Inc, Cary, USA) will be used. Descriptive statistics will be used to display baseline group characteristics. To evaluate between-group differences (i.e. the effectiveness of the HIT vs MIT intervention), a linear mixed model will be fitted with 'time' and 'group' as covariates, and incorporated random intercepts for the participants to account for the within-subject variation. To evaluate associations between diaphragm functioning and predictors/mediators for therapy success, correlations and multivariate regression analysis will be used.
This randomized controlled trial aims to investigate 1) the effects of high intensity training (HIT) compared to moderate intensity training (MIT) on diaphragm muscle strength, -endurance, -fatigue and -activation, 2) to which extent these changes in diaphragm functioning are related to changes in cardiorespiratory fitness, postural control, pain and disability after HIT versus MIT, 3) to which extent depressive mood and anxiety moderate the effects of HIT on diaphragm functioning in persons with chronic nonspecific low back pain (CNSLBP). The investigators hypothize that HIT improves diaphragm functioning more compared to MIT in persons with CNSLBP.