High-Intensity Interval Training in Young Women With Mechanical Low Back Pain

This randomized controlled trial used a two-arm parallel-group design to investigate the effects of a 4-week high-intensity interval training (HIIT) program on pain, functional disability, body composition, cardiorespiratory fitness, and quality of life in young women with mechanical low back pain.

The study was conducted at the outpatient and physiotherapy clinics of MTI University. Ethical approval was obtained from the Institutional Review Board of MTI University (approval number REC/2111/MTI.PT/2411261), and the study was conducted in accordance with the principles of the Declaration of Helsinki. The trial was retrospectively registered on ClinicalTrials.gov because of administrative delays.

Eligible participants were women aged 20-38 years with mild-to-moderate nonspecific mechanical low back pain persisting for more than three months. Participants were screened according to predefined eligibility criteria. Exclusion criteria included pregnancy or lactation, recent surgery, secondary causes of low back pain, osteoporosis, osteoarthritis, sciatica, generalized neuromuscular disorders, structural deformities, fractures, conditions restricting physical activity, cardiovascular or respiratory conditions that could compromise exercise safety, autonomic dysfunction, and use of medications that could affect heart-rate responses.

Participants were randomly allocated to either the HIIT group or the control exercise group using a computer-generated random sequence with permuted blocks of 4 and 6. Randomization was stratified according to baseline pain severity (VAS ≤5 versus >5). Allocation concealment was maintained using sequentially numbered, sealed, opaque envelopes prepared by a researcher who was not involved in participant recruitment or outcome assessment. Due to the nature of the exercise interventions, participant blinding was not feasible.

The HIIT group participated in supervised cycling sessions three times per week for 4 weeks. Each session lasted approximately 30-40 minutes and included a warm-up, repeated high-intensity cycling intervals, recovery periods, and a cool-down. High-intensity intervals were performed at approximately 80% of maximum heart rate, with heart rate continuously monitored during training. Sessions were supervised by a licensed physiotherapist.

The control group participated in supervised low- to moderate-intensity exercise consisting of stretching and treadmill walking performed at approximately 40-60% of maximum heart rate. Exercise intensity was monitored using heart-rate monitoring.

Outcomes were assessed at baseline and after completion of the 4-week intervention. Pain intensity was assessed using the Visual Analog Scale (VAS). Functional disability was assessed using the Oswestry Disability Index (ODI). Body composition, including fat mass percentage and muscle mass, was assessed using bioelectrical impedance analysis. Cardiorespiratory fitness was assessed by measuring maximal oxygen uptake (VO₂ max) using cardiopulmonary exercise testing. Quality of life was assessed using the Quality-of-Life Scale (QOLS).

Adverse events were monitored throughout the supervised exercise sessions. Participants were instructed to report symptoms including dizziness, excessive fatigue, exacerbation of musculoskeletal pain, or cardiovascular discomfort.

Statistical analyses were conducted using SPSS. Data distribution was assessed before statistical analysis. Appropriate statistical tests were used to evaluate within-group changes and between-group differences. Effect sizes were calculated to quantify the magnitude of observed differences, and statistical significance was assessed using a two-sided p-value threshold of <0.05.

**Inclusion Criteria:**

• Female participants aged 20 to 38 years.
• Mild to moderate nonspecific low back pain persisting for more than 3 months.
• Low back pain without an identifiable specific pathological cause.
• Body mass index (BMI) between 18.5 and 34.9 kg/m².
• Able to participate safely in the prescribed cycling exercise intervention.

**Exclusion Criteria:**

• Pregnancy or lactation.
• Recent surgery.
• Any chronic medical condition that restricts physical activity or exercise participation.
• Secondary causes of low back pain.
• Osteoporosis.
• Osteoarthritis.
• Sciatica.
• Generalized neuromuscular disorders.
• Structural spinal deformities.
• Vertebral or other relevant fractures.
• Reliance on assistive walking devices.
• Cardiovascular disease that could compromise safe participation in cycling exercise.
• Respiratory disease that could compromise safe participation in cycling exercise.
• Autonomic dysfunction, including diabetes mellitus.
• Current use of medications known to affect heart rate variability, including beta-blockers or calcium channel blockers.