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Life in Space for Life on Earth, ESA, Triest, 2010;

Calf muscle x-ray absorption is reduced in patients with chronic spinal cord injury, but not during 90 days of experimental bed rest

Year: 2010

Rittweger J
German Aerospace Center, GERMANY


Immobilisation leads to muscular atrophy. However, certain types of immobilisation, such as e.g. denervation can also cause a fatty degeneration of skeletal muscle. As fat has lower x-ray absorption than other soft tissues in the human body, it was hypothesized that muscular x-ray absorption (MXA) would be reduced during experimental bed rest in young healthy males.

Calf muscle cross sectional images, obtained by peripheral computed tomography (pQCT) from two previously published studies were re-analyzed. Firstly, data from 24 participants were taken from the Long Term Bed Rest (LTBR) study carried out in Toulouse between 2001 and 2003. In that study, one group engaged in resistive flywheel exercise, whilst the other participants were subjected to bed rest only. The second set of data stems from a recently completed study into anatomical changes within the tibia of people with chronic spinal cord injury (SCI) and their able bodied counterparts. Regions of interest were placed inside the calf muscle tissue in sections where the gross calf muscle cross section is greatest. LTBR data were analyzed with linear mixed effect models, with group and time as fixed factors. Data from the SCI study were analyzed by Student’s t-test.

Significant effects for group and time (P < 0.001 in both instances), but no interaction effect (P = 0.23, see Figure 1) were found for the LTBR data, with increases in MXA on day HDT28 by 2.2 (SE 0.6) HU (P < 0.001) but no change on day HDT89 (P = 0.63). In the SCI study, MXA was lower in the SCI group (15.2 HU, SD = 37.4) than in the control group (60.4 HU, SD = 5.5, P = 0.0067), with the variance of these values being greater in the SCI group than in the control group (P = 0.0045).

These findings suggest that MXA is largely reduced in patients with chronic SCI, whilst MXA is unaffected after 90 days of bed rest. It is currently unclear whether MXA is dependant on the period of exposure, or whether the more profound immobilisation in SCI is the main reason for the observed discrepancy between studies. Practically, MXA yields only very limited insights for monitoring the effects of experimental bed rest, but it could well constitute a clinical tool for assessment of the musculature in SCI patients.

Keywords: Muskeldichte, MXA
GID: 2300; Last update: 18.06.2010
More information: Original Article