Background: Low back pain (LBP) is a leading cause of disability, often requiring primary care management.

Objective: To compare the effectiveness of isometric versus isotonic exercise programs for LBP.

Methods: Sixty adults with LBP were randomly assigned to two groups. Group A (n=30) performed isometric exercises, infrared therapy, and TENS. Group B (n=30) performed isotonic exercises with the same adjunct therapies. Pain (VAS), disability (MODI), and abdominal endurance were measured pre- and post-intervention.

Keywords: Exercise therapy; low back pain; disability evaluation

Group-Specific Exercise Protocols:

• Isometric Exercise Group (IEG): This group performed a circuit of three core-stabilizing isometric exercises, each held for 10 seconds with brief rest intervals, for 5 complete repetitions. The exercises included: (a) Isometric Curl-Up, (b) Side Bridge, and (c) Bird Dog. The total dedicated exercise time was approximately 20 minutes per session.
• Isotonic Exercise Group (ITG): This group performed a circuit of three dynamic, strength-oriented isotonic exercises, each completed for 10 repetitions. The exercises included: (a) Bent Knee Sit-Up, (b) Cross Curl-Up, and (c) Prone Back Extension. The total dedicated exercise time was also approximately 20 minutes per session. All exercises were selected and adapted from previously published rehabilitation protocols for CLBP [13].

Adjunctive Therapies (Common to Both Groups):

1. Infrared (IR) Therapy: A standard therapeutic infrared lamp was positioned 50 cm from the participant's lumbar spine at a 90-degree angle. Heat was applied for 15 minutes per session to promote muscle relaxation and local blood flow.
2. Transcutaneous Electrical Nerve Stimulation (TENS): Electrodes were placed over the painful lumbar area. A low-frequency (<10 Hz) TENS unit was applied for 20 minutes per session. The analgesic mechanism of TENS is well-documented, involving the modulation of pain pathways via opioid and noradrenergic receptors in the central nervous system [16].

Both groups received a standardized four-week intervention program, consisting of three supervised sessions per week, totaling 12 sessions. Each 55-minute session included adjunctive therapies common to both groups, followed by the specific exercise protocol.

Inclusion Criteria:

• Age between 18 and 60 years;
• Diagnosis of non-specific CLBP, defined as pain localized between the lower rib margin and the gluteal folds persisting for more than three months;
• Self-reported pain intensity score between 40 mm and 80 mm on a 100-mm Visual Analogue Scale (VAS), indicating moderate to severe pain;
• Pain experienced on at least three days in the month preceding enrollment, with documented interference in daily activities;
• A formal referral for physiotherapy management.

Exclusion Criteria:

• The presence of "red flag" pathologies (e.g., spinal tumor, infection, fracture); - Neurological signs or symptoms suggestive of radiculopathy or myelopathy;
• a history of spinal surgery or epidural steroid injections within the previous 12 months;
• Systemic inflammatory diseases (e.g., rheumatoid arthritis) or major neurological disorders;
• Pregnancy;
• Receipt of physiotherapy for low back pain within the last six months;
• Current use of non-steroidal anti-inflammatory drugs (NSAIDs) or inability to refrain from their use during the study period;
• Any diagnosed psychiatric condition.