Low back pain is a common disorder, occurring worldwide in both males and females in all age groups1. The prevalence is higher in females and the incidence peaks between 30 and 65 years. It is currently the most frequent musculoskeletal cause of functional disability and it has a major socio-economic impact on today's society. Although a small percentage of persons with low back pain can be diagnosed with a specific underlying cause, almost 90% of persons with low back pain present with symptoms of nonspecific origin. A part of these symptoms are only of short duration, but 23% of all people will develop nonspecific chronic low back pain (NSCLBP).

Exercise therapy (ET) is currently an important component in the treatment of NSCLBP. Previous studies analysed the effects of various modes of exercise therapy, such as motor control therapy, core stability training and aerobic conditioning training. However, therapy outcomes can be low, and guidelines in favour of using a specific program are contradictory. It thus still remains unclear which therapy modality is best suited. Furthermore, no recommendations are available about optimal training intensities during rehabilitation of persons with NSCLBP.

Since as well aerobic as muscular deconditioning are apparent in persons with chronic low back pain and improvements in overall physical fitness can affect therapy outcomes in this population, ET specifically focussing on physical fitness can be advocated for NSCLBP rehabilitation. High Intensity Training (HIT), has been promoted as an effective and efficient training method for improving physical fitness and health related parameters in healthy persons. Also, HIT resulted in successful reconditioning and improvement of functional and disease related outcomes in persons with other chronic diseases such as multiple sclerosis, heart failure, COPD and cardiometabolic diseases. Although some studies showed promising results for the effect of HIT on low back pain such as high intensity isolated, evidence is still scarce and study results are unclear because of methodological shortcomings.To evaluate HIT for the rehabilitation of persons with NSCLBP, a therapy program was developed consisting of high intensity interval cardio and high load whole body strength training.

The aim of this pilot study is 1) to evaluate the feasibility of a HIT program for the rehabilitation of persons with NSCLBP, and 2) to evaluate the effects of a HIT program on disease related outcomes and physical fitness compared to a conventional rehabilitation program in persons with NSCLBP.

Inclusion Criteria:

1. medically diagnosed with non-specific chronic low back pain4,
2. over 18 years old,
3. able to understand Dutch (spoken and written).

Exclusion Criteria:

1. invasive surgery at the lumbar spine in the last 18 months (arthrodesis was excluded, microsurgery was allowed),
2. radiculopathy (uni- or bilateral),
3. co-morbidities: paresis and/or sensory disturbances by neurological causes, diabetes mellitus, rheumatoid arthritis, an increase of pain of 3 points with a result of > 8/10 on the Numeric Pain Rating Scale (NPRS) in the last 48 hours, pregnancy,
4. ongoing compensation claims and/or (work)disability > 6 months,
5. rehabilitation/exercise therapy program for LBP in the past 6 months.