The human body is simply amazing. While we might know how many bones we have or how the immune system fights off diseases, it's sometimes hard to grasp without seeing physical examples. A video shared by user ExpertAccident on Reddit showcases one of these mind-boggling actions. The footage features a medical model and demonstrates how the bones of the forearm move; specifically, how the radius rotates over the ulna when we twist our forearm.
The video draws the curtain on this motion, apparently simple and commonplace—you may have done it a dozen times today—revealing how the intricate bone structure operates for you to merely twist your arm. Just turning your hand upside down requires your bones to contort, doing so seamlessly and without causing you discomfort. To do so, the ulna (the straight bone on the little finger side of your forearm) stays in the same place while the radius (the curved bone on the thumb side) rotates around it.
The video got a lot of attention on Reddit thanks to the universality of the topic and the startling picture it paints of what happens inside our forearms with even the gentlest of movements. “I definitely just did this motion with one arm while holding my phone in the other. Like 10 times,” said one user, to which someone replied, “And for some reason the bones feel more comfortable crossed right? I can't unfeel it now and it's making me uncomfortable. I'm not the only one right?”.
People said they groped their arms trying to perceive the switch, or simply stated that it looked painful. However, not everyone can do this, so it's best to appreciate it—no matter how weird it looks. “So my bones are ‘stuck' in the twisted motion,” said one user. “Can't rotate my wrist at all. For those who are able to—appreciate your weird twisty and untwisty bones!”
A video shared on Reddit shows how the bones of the forearm move; particularly, how the radius rotates over the ulna when we twist our forearm.