Fascia can be finicky: It gets stiff and sticky when you don't move around enough, but it can also get bound up and twisted when you move too much or do repetitive motion or injure yourself through activity, says James L. Thornton, the president of the National Athletic Trainers Association.
The fix: Work out overused sore spots with a foam roller. You've probably seen people at the gym using these things, which look like pool noodles, to stretch their back, hamstrings and the notoriously tight IT band on the outside of the hips (this video from Jeff Richter, certified strength and conditioning coach at St. Vincent Sports Performance in Indianapolis, provides a good foam-roller tutorial). Thornton says to go slowly, and when you get to a sore spot that feels like a bruise, pause for 15 to 20 seconds. The discomfort should melt away as the fascia softens and the muscles release. If you feel intense pain that doesn't dissipate, Thornton says to stop and consider making an appointment with a physical therapist. At home, you can try a device called the Stick—instead of laying your body on top of it, you roll it against your muscles (this video shows how). The stick lets you really go deep into your calves, shins and hamstrings, but because it's more rigid than a foam roller, it can feel much more intense (think deep-tissue massage versus regular rubdown).