Low back pain is a significant public health problem, is very prevalent, and is often characterized by the persistence of symptoms. Unfortunately, substantial improvements in people with chronic low back pain are rare, causing most people to live with the pain. People with chronic low back pain may have an exaggerated pain response to nociceptive input into tissues that may also cause symptoms distant from the site of the primary symptoms. Historically, these symptoms were thought to be related to pathoanatomic changes to the muscles, ligaments, or joints. However, the severity of these structural changes weakly correlates with the clinical presentation and, in most cases, is not directly related to diagnostic image findings. Patients with chronic musculoskeletal pain, in general, show signs of local/central sensitization. The central sensitization may appear to be directly correlated with the intensity and duration of pain. Therefore, it is essential to reduce pain intensity and minimize the duration of pain to prevent this from happening.

Pain relief for chronic low back pain patients should be aimed at treatments that reduce central excitability and increase central inhibition. Research into chronic low back pain treatment has demonstrated strong evidence that different types of exercise decrease pain and improve quality of life. However, exercise itself may be painful, preventing a person from exercising. Thus, treatments aimed at decreasing pain will improve a person's ability to exercise and participate in activities of daily living.

One treatment aimed at reducing central excitability and increasing central inhibition is transcutaneous electrical nerve stimulation (TENS). TENS is a "non-pharmacological" treatment for pain that is inexpensive, safe, and easy to use. Prior studies show that TENS utilizes opioid receptors both spinally and supraspinally to inhibit nociceptive dorsal horn neurons, reduce excitatory neurotransmitter release, and reduce hyperalgesia. Thus, TENS may be particularly useful in people with chronic low back pain because it can activate descending inhibitory pathways (reduced in chronic low back pain patients) and inhibit central excitability (increased in chronic low back pain patients).

Previous studies that have investigated the effects of TENS on pain in low back pain patients have failed to use proper intensities of current, and the assessment of pain was not performed during the peak of the analgesic response. Previous studies show inadequate intensities do not reduce pain or increase pressure pain thresholds. Further, TENS typically does not affect resting pain, while changes in pressure pain thresholds and pain with movement are reduced. Thus, the current study proposes to assess the effects of TENS on measures of pain, function, and descending inhibition using the maximal tolerable intensity of TENS applied to a large area of the trunk.

The study will be a simple crossover design with the following three treatments (1) active TENS, (2) placebo TENS or (3) no treatment control randomly assigned. Each subject will receive all 3 interventions in random order.

The following tools will be used to measure pain (Numeric Rating Scale), central excitability (pressure pain thresholds, temporal summation and CPM) and function (sit-to-stand test and repeated trunk flexion).

Inclusion Criteria:

• people who have experienced back pain for at least 3 months
• and have reported a minimal pain level of 3 on the 0-10 Pain Numerical Rating Scale (NRS)
• age from 18-60
• TENS naive or have not used TENS for 5 years.
• Both men and women may participate in the study

Exclusion Criteria:

• Serious spinal disorders, such as fractures, tumors, or inflammatory arthritis disease
• nerve root disorders confirmed by neurological tests;
• neurological diseases
• severe cardiorespiratory disease
• pregnancy
• skin infection or lesions or change in sensation at the TENS application site
• cancer
• cardiac pacemaker
• allergy to electrodes
• use of opioids.