Pick up a coin. Button a shirt. Type a text message.

It feels like your fingers are doing all the work. Surprisingly, they contain no muscles at all.

Instead, almost every movement comes from muscles in your forearm and the palm of your hand. 

Those muscles pull on long, strong tendons that run through your wrist and into your fingers. Think of them as biological cables. When a muscle contracts, it pulls on a tendon, causing a finger to bend, straighten, or grip.

This design solves a major engineering problem. Muscles take up space. If each finger were packed with muscle, your hands would be thicker, heavier, and far less nimble. By placing most of the muscles farther up the arm and connecting them with tendons, your body gives you fingers that are both slim and capable of astonishing precision.

That is why the same hand can crack open a jar, thread a needle, play a piano concerto, or perform delicate surgery. The muscles provide the power. The tendons deliver it exactly where it is needed.

There is one small exception. The fleshy pad at the base of your thumb contains several muscles that help give the thumb its extraordinary range of motion. Even so, the thumb itself, like your other fingers, contains no muscle tissue.

If your fingers feel tired after a long day of typing, gardening, or playing guitar, the muscles responsible are working mostly in your forearms, not inside your fingers.