Astronauts Can Come Home Taller
Bruce McCandless II during an untethered spacewalk, 1984. NASA, public domain. This photograph illustrates orbital free fall; it is not a measurement of spinal growth. Source and rights.
An adult astronaut leaves Earth at one height and can return a little taller. It sounds like an unexpected benefit of a very long trip.
But this is not a late growth spurt. The change is temporary, and the bones have not simply stretched into longer versions of themselves.
What changes when the body spends months without its usual gravitational loading?
The spine is not a stack of solid blocks
Between the vertebrae are discs that contribute to the spine’s flexibility and cushioning. Its overall length also depends on its curves and the loading placed on it.
In microgravity, that loading changes. NASA describes spinal elongation involving changes in curvature and the intervertebral discs. A small change repeated along the spine can become a noticeable change in overall height.
Side view of the vertebral column from Gray’s Anatomy (1918), illustration by Henry Vandyke Carter, later colorized by Uwe Gille. Public domain. Source and rights.
A measuring tape is not the whole investigation
NASA reports that crew members on long-duration missions can become up to about three percent taller, then return to their normal height on Earth. “Up to” matters: it is not an identical gain promised to every astronaut.
The agency has used spinal ultrasound aboard the International Space Station to investigate what is happening. An apparent increase in height raises questions about the spine’s structure and function, not just the number on a chart.
The effect also matters to equipment. NASA’s spacesuit education materials describe allowing for spinal lengthening when considering suit fit. A body measured before launch may not keep precisely the same proportions throughout a mission.
Garrett Reisman uses the station’s resistance-exercise equipment, May 11, 2008. NASA, public domain. Exercise helps counter the loss of normal weight-bearing loads. Source and rights.
We experience a small everyday version
A NASA discussion of human spaceflight notes that unloading the spine while lying down can make a person a little taller in the morning than later in the day. The spaceflight effect takes that familiar principle into a very different environment.
This does not mean space is a convenient height treatment. Microgravity brings numerous physical challenges, and researchers study these changes to protect crews and design equipment that fits them.
Being an adult does not make the body’s dimensions perfectly fixed. Some depend on what the body is being asked to support.
Sources and image credits
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