The effects of rehabilitation on the muscles of the trunk following prolonged bed rest

Abstract

Microgravity and inactivity due to prolonged bed rest have been shown to result in atrophy of spinal extensor muscles such as the multifidus, and either no atrophy or hypertrophy of flexor muscles such as the abdominal group and psoas muscle. These effects are long-lasting after bed rest and the potential effects of rehabilitation are unknown. This two-group intervention study aimed to investigate the effects of two rehabilitation programs on the recovery of lumbo-pelvic musculature following prolonged bed rest. 24 subjects underwent 60 days of head down tilt bed rest as part of the 2nd Berlin BedRest Study (BBR2-2). After bed rest, they underwent one of two exercise programs, trunk flexor and general strength (TFS) training or specific motor control (SMC) training. Magnetic resonance imaging of the lumbo-pelvic region was conducted at the start and end of bed rest and during the recovery period (14 and 90 days after re-ambulation). Cross-sectional areas (CSAs) of the multifidus, psoas, lumbar erector spinae and quadratus lumborum muscles were measured from L1 to L5. Morphological changes including disc volume, spinal length, lordosis angle and disc height were also measured. Both exercise programs restored the multifidus muscle to pre-bed-rest size, but further increases in psoas muscle size were seen in the TFS group up to 14 days after bed rest. There was no significant difference in the number of low back pain reports for the two rehabilitation groups (p=.59). The TFS program resulted in greater decreases in disc volume and anterior disc height. The SMC training program may be preferable to TFS training after bed rest as it restored the CSA of the multifidus muscle without generating potentially harmful compressive forces through the spine.

Fig. 1

Muscle cross-sectional area measurements. Left of image Cross-sectional area measurements were made of the psoas (PS), erector spinae (ES) and multifidus (MF) muscles from L₁ to L₅. Quadratus lumborum (QL) was measured from L₁ to L₄ as it was typically absent at L₅. Arrows indicate the fascial border between MF and ES which aided delineation of these two muscles. Right of image Positioning of images at each vertebral level

Fig. 2

Measurements of spinal morphology. Left End of 60 days bed rest; right end of rehabilitation phase (90 days after end of bed rest) in the same subject. Disc volume was interpolated from sagittal plane disc area measurements of each lumbar intervertebral disc (shown at L_3/4 on left side of image). Anterior and posterior disc height was also measured (shown between L_2/3 at left). The lumbar lordosis angle was calculated between lines drawn at the superior endplate of L₁ and S₁. Spinal length (right) was measured between the dorsorostral corner of S₁ and L₁