Table 1 Inclusion and exclusion criteria

Inclusion criteria

1. Between 18 and 50 years of age

2. Answer “yes” to the following questions:

▪ Have you had two or more episodes of low back pain (LBP) in the past 12 months with at least one of the episodes causing a restriction of work or leisure time activity?

3. Body mass index between 17 and 37 kg/m²

4. With no condition that could limit participation in supervised resistance training exercise based on the Physical Activity Readiness Questionnaire (PAR-Q)

5. Sedentary lifestyle as measured by a classification of “low” or “moderate” levels of physical activity based on scoring criteria of the International Physical Activity Questionnaire (IPAQ)

6. Exhibit low trunk extensor endurance defined as a time to task failure during the modified-Sorensen test of <176 seconds.

Exclusion criteria

1. Participate in progressive resistance exercise within the previous 24 weeks prior to screening

2. Experienced limb amputation (except for toes) and/or any fracture within 24 weeks

3. Have a personal history of the following neurological disorders: Alzheimer’s disease, amyotrophic lateral sclerosis, multiple sclerosis, Parkinson’s disease, or stroke

4. Have a personal history of the following cardiorespiratory disorders: congestive heart failure, myocardial infarction, or peripheral vascular disease

5. Have conditions (e.g., myasthenia gravis, myositis, muscular dystrophy or myopathy, including drug-induced myopathy) leading to muscle loss, muscle weakness, muscle cramps or myalgia

6. Have a personal history of the following musculoskeletal disorders: rheumatoid arthritis, spinal or pathological fractures, scoliosis, spondylolisthesis, avascular necrosis or osteonecrosis, severe osteoarthritis. (Including a history of spinal surgery or a hip arthroplasty).

7. Have a personal history of any of the following conditions or disorders not previously listed: diabetes, fibromyalgia, active cancer, severe obesity (i.e., body mass index greater than 35 kg/m²), clinical depression (i.e., subjects who score 24 or higher on the Center for Epidemiology Depression Scale)

8. Have chronic or relapsing/remitting gastrointestinal disorders such as inflammatory bowel diseases, irritable bowel syndrome or gastrointestinal infections within 28 days of screening

9. Have an acute viral or bacterial upper or lower respiratory infection at screening

10. Have moderate or severe chronic obstructive pulmonary disease

11. Report back pain greater than 4 (on a 10- point numerical pain rating scale) at screening

12. Have a leg length discrepancy >3 cm

13. Exhibit abnormal or uncontrolled blood pressure (BP) at the screening visit (i.e., diastolic BP >100 and/or systolic BP >160 mmHg). If taking anti-hypertensive medication, have to be on stable doses of medication for more than 3 months

14. Exhibit abnormal electrocardiogram findings indicative of left ventricular hypertrophy (based on Cornell voltage criteria) at the screening visit

15. Have a current or recent history (within 1 year of screen) of heavy alcohol consumption (men ≥21 drinks/week, 4 drinks/day; women ≥14 drinks/week, 3 drinks/day) or drug abuse

16. Have a current or previous use of any drugs known to influence muscle mass or performance within 24 weeks

17. Report being pregnant, lactating, or that they anticipate becoming pregnant in the next year

18. Report unexplained weight loss over the past month (>10 lbs)

19. Report they have pending litigation related to an episode of LBP or are receiving any type of disability services

20. Use of systemic glucocorticoids within 12 weeks prior to screening

21. Report having received any treatment for LBP by a health care practitioner in the past 6 weeks22. Have contraindications for exposure to a magnetic field