It’s pretty remarkable that human beings are able to function in zero gravity. After all, at every point in the evolutionary history of life on Earth, gravity was present, so it’s not a given that we’d be able to make do without it. Thanks to our adaptable brains, however, shifting to an alien environment like microgravity isn’t completely debilitating. For example, our sense of balance relies on the gravitational pull of the Earth to function, and when it’s sidelined, our sense of sight steps in to compensate.
You can witness this compensation in action by watching Christina Koch from the Artemis II mission trying to walk with her eyes closed after returning to Earth. After relying on her vision for balance for 10 days, it’s a bit of a struggle to stay upright without that sensory input.
Grip strength is another human faculty that’s affected by gravity, albeit indirectly. That’s because it’s tightly linked in our brains to perceived load force, or the amount of “oomph” we think we need to lift something. A new study published in The Journal of Neuroscience shows that this link is disrupted when gravity disappears, but our brains can still adjust.
To find out how weightlessness affects grip strength, neuroscientists from the Université catholique de Louvain in France and Ikerbasque, the Basque Foundation for Science, in Spain tracked how astronauts manipulated sensor-laden objects by moving them up and down and back and forth at different paces both pre-flight, during zero gravity, and post-flight.
Read more: “When Gravity Breaks Down”
They found that astronauts tended to overcompensate their grip strength when moving objects around in space. For example, when moving the object upward, they clamped down, as if expecting it to fly away. After they returned to Earth, astronauts initially made the same “errors”—even reporting the objects were heavier than they thought—but eventually adjusted.
Researchers say that the tighter grip force in microgravity comes from a very human instinct—the inclination to avoid accidents. The greater the kinetic energy of an object, the greater the risk to equipment and crew if it slips out of control. By tightening their grips, the astronauts were mediating that risk as best they could. After landing back on Earth, it took some time to readjust to gravity and re-establish the link between grip force and load force.
It’s remarkable when you think about it. Despite no experience with weightlessness, evolution still somehow gave us a brain capable of adapting to it. 
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Lead image: Icon_gallery and sKjust / Adobe Stock
