The human body in space is a fascinating subject, and the phenomenon of astronauts returning home temporarily taller than when they left is a captivating aspect of this field. But what does this mean for the health of these spacefarers, particularly when they return to Earth? This article delves into the science behind this phenomenon, explores its implications, and examines the challenges that arise when astronauts return to gravity. It also highlights the need for further research and understanding of the long-term effects of microgravity on the human body.
One of the most intriguing aspects of this phenomenon is the role of the intervertebral discs. The standard explanation for the increase in height is the swelling of these discs in the absence of compressive load. However, recent MRI studies have cast doubt on this theory. In a study of six crewmembers who spent six months on the International Space Station (ISS), researchers found that lean paraspinal muscle content fell significantly, but lumbar disc heights showed no appreciable difference. This suggests that the swelling of the discs is not the primary cause of the increase in height.
So, what is the explanation? The answer lies in the natural curve of the spine. Without gravity, the spine straightens, and a straighter column is a longer one. This is supported by the fact that spacecraft seats and spacesuits are designed with an allowance of 2.54 centimeters added to the torso length as standard. This design constraint highlights the importance of understanding the effects of microgravity on the human body.
The implications of this phenomenon are far-reaching. For one, it raises concerns about the health of astronauts when they return to Earth. The Skylab 4 crewmember whose height was tracked by William Thornton reported back pain on landing day, associated with a herniated disc. This is supported by studies showing a higher incidence of disc injuries in astronauts compared to matched controls. The dataset behind these studies, NASA's Longitudinal Study of Astronaut Health, covering 321 astronauts from April 1959 to December 2006, reveals that Apollo-era and Shuttle crews had a higher incidence of disc injury than ISS and Mir crews.
This highlights the need for further research and understanding of the long-term effects of microgravity on the human body. In particular, there is a need for contemporary reports of in-flight back injury and recent studies of post-flight injury incidence. This will help to better characterize the size of the current risk under current exercise regimes.
In conclusion, the phenomenon of astronauts returning home temporarily taller than when they left is a fascinating aspect of human physiology in space. However, it also raises important questions about the health of these spacefarers when they return to Earth. Further research is needed to better understand the long-term effects of microgravity on the human body and to develop effective countermeasures to mitigate these effects.
