Even when you’re just bending your elbow without twisting your hand, the muscle that normally turns your palm down still turns on — maybe to balance out other muscles that are pulling the wrong way.

Even when you're just bending your elbow without twisting your forearm, a muscle called pronator teres still turns on — not to twist anything, but to help balance out other muscles so your movement stays smooth. The study saw this happen and says it’s like a helper muscle keeping things steady.