Tendons are found at the end of a muscle. Your muscle has to turn into a tendon in order for it to be able to attach to a bone. When your muscle contracts (shortens), it pulls on the tendon which in turn pulls on the bone to cause movement.

If your tendon it irritated or swollen, as in tendinitis, then the pull on the tendon will hurt and may not cause a successful movement. If your tendon is torn, no matter how hard your muscle contracts the bone will not move.