According to Sarno, TMS is a condition in which unconscious emotional issues (primarily rage, though other practitioners include other subconscious emotional issues such as anxiety, past trauma, and fear) initiate a process that causes physical pain and other symptoms. His theory suggests that the unconscious mind uses the autonomic nervous system to decrease blood flow to muscles, nerves or tendons, resulting in oxygen deprivation (temporary micro-ischemia) and metabolite accumulation, experienced as pain in the affected tissues.[2][8][11] Sarno theorized that because patients often report that back pain seems to move around, up and down the spine, or from side to side, that this implies the pain may not be caused by a physical deformity or injury.[7]

Sarno stated that the underlying cause of the pain is the mind's defense mechanism against unconscious mental stress and emotions such as anger, anxiety and narcissistic rage. The conscious mind is distracted by the physical pain, as the psychological repression process keeps the anger and rage contained in the unconscious and thereby prevented from entering conscious awareness.[12][13] Sarno believed that when patients recognize that the symptoms are only a distraction, the symptoms then serve no purpose and subsequently go away. TMS can be considered a psychosomatic condition and has been referred to as a "distraction pain syndrome."[14]

Sarno was a vocal critic of conventional medicine with regard to diagnosis and treatment of back pain, which is often treated by rest, physical therapy, exercise and/or surgery