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Space & Astronomy
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The Space Stretch: Unpacking the Science Behind Why Astronauts Get Taller in Orbit
A peculiar side effect of space travel is a temporary growth spurt. In microgravity, the discs between an astronaut's vertebrae expand, freed from Earth's constant compression. This spinal decompression can add up to two inches in height, a fascinating change that reverses upon returning home.
Leaving Earth behind is a transformative experience in every sense of the word. For astronauts, it reshapes their perspective, their understanding of the cosmos, and, quite literally, their own bodies. Beyond the well-documented muscle atrophy and bone density loss, one of the most curious physiological changes is also one of the most surprising: astronauts grow taller in space.
Down to the Backbone: The Mechanics of Spinal Elongation
To understand this phenomenon, we have to look at the human spine. It isn't a single, rigid bone but a complex column of 33 vertebrae stacked one on top of the other. Separating most of these bones are soft, gelatinous, cartilage-filled cushions called intervertebral discs. On Earth, gravity is a relentless force, constantly pushing down on us. This constant compression squeezes our spinal discs throughout the day, forcing out fluid. It's why you are technically slightly shorter in the evening than you are when you first wake up in the morning after your discs have had a chance to decompress overnight.
Microgravity's Magic Trick
Now, imagine removing that constant gravitational pressure almost entirely. In the microgravity environment of the International Space Station (ISS), the spine is no longer being compressed. Freed from this load, the intervertebral discs can relax, expand, and absorb more fluid, much like a sponge soaking up water. This expansion increases the space between each vertebra, leading to a cumulative increase in the total length of the spinal column. The result? Astronauts can gain up to 3% of their initial height, which for a six-foot-tall person translates to a temporary growth spurt of nearly two inches (about 5 centimeters).
The Not-So-Fun Side Effects
While gaining a couple of inches might sound like a neat party trick, it's not without its downsides. The elongation of the spine also straightens its natural, gentle 'S' curve. This stretching and shifting can lead to significant discomfort and back pain for astronauts while in orbit. More critically, researchers are studying the health implications for when they return to Earth. The deconditioned muscles supporting the newly-lengthened spine, coupled with the reintroduction of gravity, may increase the risk of injuries like a herniated disc. To better understand these changes, NASA has conducted experiments like the Spinal Ultrasound investigation aboard the ISS. As the principal investigator, Dr. Scott A. Dulchavsky, noted:
This is a new data point for us using a new technology in a new environment... The Spinal Ultrasound investigation is the first to use this technology in space to evaluate the effects of microgravity on the spine.
This research is vital, as it helps scientists develop countermeasures to protect astronaut spinal health, not just during their mission but after they've landed.
Coming Back Down to Earth
The extra height is, of course, temporary. Once an astronaut returns to Earth, gravity immediately begins its work again. The spine starts to recompress, and within a few days to weeks, the astronaut is back to their original height. The phenomenon gained some viral attention in 2018 when Japanese astronaut Norishige Kanai humorously tweeted he had grown 9 cm (about 3.5 inches), only to correct himself later, stating the actual growth was a more typical 2 cm. His story highlights just how noticeable this change can be for those experiencing it firsthand.
Ultimately, the 'space stretch' is a powerful example of the human body's incredible adaptability. It's also a crucial piece of the puzzle for scientists planning long-duration missions, like a journey to Mars. Understanding how to mitigate the negative effects of spinal elongation will be essential for ensuring the crew arrives healthy, stands tall, and is ready for humanity's next giant leap.