This single-centre, parallel-group randomized controlled trial will test whether one session of moist hot-pack therapy produces immediate improvements in pain intensity and lumbar erector spinae muscle stiffness in adults with nonspecific low back pain. Participants are randomized 1:1 to hot-pack or sham (room-temperature pack). Outcomes are assessed at baseline and immediately after the session using VAS (0-10 cm) and MyotonPro; a short follow-up (24-48 h) captures Oswestry Disability Index (ODI) and perceived change. The intervention is brief, low-risk, and commonly used in clinical practice, yet high-quality evidence on its acute effects is limited.

Rationale. Hot-pack (thermotherapy) is frequently prescribed to reduce pain and muscle tension in low back pain, but controlled evidence quantifying immediate changes in muscle mechanical properties and pain remains scarce. Demonstrating short-term benefits with objective measures (MyotonPro) and validated scales (VAS, ODI) could inform pragmatic care pathways for nonspecific low back pain.

Objectives and Hypotheses. Primary objective: determine whether a single hot-pack session reduces erector spinae stiffness (MyotonPro) and pain (VAS) versus sham. Secondary objective: explore short-term effects on functional disability (ODI) and perceived improvement. We hypothesize greater immediate reductions in stiffness and pain, and better short-term function, with hot-pack versus sham.

Design and Setting. Prospective, two-arm, parallel RCT at Atatürk University Faculty of Medicine (Physical Medicine & Rehabilitation / Orthopedics). Target sample: 30 adults (pilot). Allocation is 1:1 using computer-generated randomization; outcome assessors and participants are blinded.

Participants. Adults 18-65 y with nonspecific/mechanical low back pain and baseline VAS ≥ 3/10. Key exclusions include pregnancy, pacemaker/implanted devices, recent lumbar surgery or heat/cold therapy (<6 weeks), dermatologic lesions, neurologic deficit, tumour, or systemic inflammatory disease. Written informed consent is obtained before any procedure.

Interventions.

Hot-pack (Active): Moist hot-pack at 60-65 °C applied over the lumbar region for 20 minutes with a 6-8 towel barrier. Skin is checked at minutes 5 and 10.

Sham (Comparator): Identical setup using a room-temperature pack (no heat).

Outcome Measures and Timing.

Primary: Change in pain intensity (VAS, 0-10 cm) from pre- to immediate post-intervention.

Key Secondary: Change in erector spinae stiffness (MyotonPro) from pre- to immediate post-intervention; ODI at 24-48 h; patient-reported perceived change.

Procedures. After screening and consent, baseline demographics and outcomes are recorded. MyotonPro measurements are taken over the lumbar erector spinae at L3-L4, 2-3 cm lateral, with three repeats per point and averaged. Post-session, VAS and MyotonPro are repeated; ODI and a brief perceived-change item are collected 24-48 h later. All assessments are performed by trained physiotherapists following device protocols and the Declaration of Helsinki.

Randomization, Masking, and Data Handling. Randomization is computer-assisted (1:1). Participants and assessors are blinded to group assignment via a sham procedure mirroring the active setup. Data are recorded with coded IDs and analysed with mixed-model repeated-measures ANOVA (group × time), reporting effect sizes and 95% CIs.

Inclusion Criteria:

• Adults aged 18-65 years

Nonspecific/mechanical low back pain (clinical diagnosis)

Baseline pain ≥3/10 on a 0-10 Visual Analogue Scale (VAS)

Able to understand procedures and provide written informed consent

Able to attend baseline, immediate post-session, and 24-48 h follow-up assessments

Exclusion Criteria:

• Neurologic deficit, tumour, or systemic inflammatory disease

Prior lumbar spine surgery

Heat or cold therapy to the lumbar region within the past 6 weeks

Dermatologic lesions, open wounds, or skin conditions over the lumbar area

Contraindications to heat (e.g., impaired sensation/neuropathy over the area, severe circulatory disorders)

Pregnancy

Implanted electronic devices (e.g., pacemaker)

Inability to comply with the study schedule or procedures

No plan to share individual participant data. Only aggregate findings will be reported in publications and at ClinicalTrials.gov.

Participants receive either a heated moist pack or an identical setup with a room-temperature pack; identical towel barriers and procedures maintain participant blinding. The treating therapist cannot be blinded due to the nature of heat delivery. Outcome assessors are blinded to allocation; data are recorded with coded IDs to preserve blinding during analysis