Origin of back pain during bedrest: A new hypothesis.

Back pain during bed rest has frequently been reported. Until recently, studies concentrated mainly on length changes of the spine. Functional aspects such as reduced movements of the back, although anecdotally reported, could neither be quantified nor were they taken into account as a potential cause of back pain. In the present study the geometry of the spinal columns of eight healthy men was continuously recorded over 24 h before, during, and after a seven-day 6 degree head-down tilt period (Series 1). The approach is based on the measurement of skin distances between four pairs of miniaturized ultrasound transmitters and receivers fixed on the back in parallel to the thoracic and lumbar spine. After a four-week break, the entire study was repeated with the same subjects (Series 2). The major findings are: 1. The length increase of the spine segments investigated was virtually identical in both series. 2. During the bedrest period significantly greater pain occurred in Series 1 as compared to Series 2. Pain was generally confined to the lumbar region about 10 cm lateral of the spinous processes. 3. Pain was most prominent when trunk motions were minimal, while movements over the maximal range of the spine transiently reduced the pain remarkably. 4. During bed rest, the amplitude of voluntary movements of the lumbar segment was reduced in particular during Series 1. It is concluded that back pain during bed rest is induced by reduced amplitudes of spine movements rather than by increases in the spine length. It is suggested that isometric muscle contractions of low intensity are a primary course of back pain. Regular, slow, large-amplitude movements of the spine are recommended as a countermeasure.