It starts as a gentle, nagging pain. You can almost ignore it and keep pushing your way through the workout. After all, athletes regularly work through pain. Push yourself too far, though, and now your Achilles tendon is throbbing. The pain reduces you to walking on your tiptoes to avoid stretching the tendon. What was once a minor ache, now has you parked on the couch with your foot perched on a heap of ice.