Physiologically, most muscles relax during non-rapid eye movement (NREM) sleep and become atonic (i.e., exhibiting a lack of muscle tone similar to paralysis) during rapid eye movement (REM) sleep, except for the ocular muscles and the diaphragm. This atonia prevents us from moving around and hurting ourselves during sleep, but it can also contribute to the etiology of certain sleep disorders, such as narcolepsy.
Musculoskeletal disorders of the bones, joints, and muscles — like arthritis, fibromyalgia, or chronic back pain — can result in pain that interferes with the ability to sleep. This problem with sleep leads to fatigue, interferes with the person’s quality of life, and can make their pain worse.1 Treating such pain and insomnia concurrently — rather than sequentially — yields better outcomes for both conditions, compared to maximizing treatment for one condition and subsequently adding treatment for the second.
- Institute of Medicine (IOM) Committee on Sleep Medicine and Research, Colten HR and Altevogt BM (ed.), Sleep Disorders and Sleep Deprivation: An Unmet Public Health Problem, Washington, DC: National Academy of Sciences, 2006.