Comment on Matsumura et al.: changes in water content of intervertebral discs and paravertebral muscles before and after bed rest

Abstract

I read the article in your journal by Matsumura and colleagues [1] with great interest. Their main findings were, based upon magnetic resonance imaging scans, that after 4 h bed-rest in 20 individuals, increases in lumbar disc water content and decreases in lumbar paravertebral muscle water content occurred. As the authors state in their discussion, the findings of increased disc water content are largely in line with what we might expect, based upon the impact of normal diurnal disc loading patterns on disc water content [2]. However, the changes in paravertebral muscle water content with lying have not, prior to the work by Matsumura and colleagues, previously been studied. It is known that muscle size can be affected by changes in body posture. For example, after 24 h lying [3], a decrease in calf muscle size, but increase in neck muscle size, has been observed. It could be presumed these changes are associated with changes in muscle water content, but this idea was not confirmed by the same authors’ [3] examination of T2-time in the musculature. The existing literature [4–7] largely shows that upon lying, body fluid volume in the legs reduces and increases in the head and thoracic region. Conventional wisdom, at least in discussions with my colleagues, has been that the lumbar region should be a neutral point where no net loss or increase of fluid should occur with lying. For these reasons, the findings of Matsumura and colleagues of decreased paravertebral muscle water content after 4 h lying surprised me. To help to better understand the findings of Matsumura and colleagues, it would be helpful to have data on the following: