For most people, the hamstrings tend to be weak and underused, says Bezner. Target the hamstrings with a leg curl.
How to: Stand facing a wall, up against it. Slowly bend one leg, up toward your buttocks, about 90 degrees, then straighten it again. (The wall keeps your thigh from moving forward, preventing your body from recruiting your hip flexor for help, Bezner says.)
Too tough? Try it lying down on your stomach. Too easy? Add resistance: Use an ankle weight. Or take that band and secure one end to a stable anchor (like a leg of your bed), and attach the other end around your foot. Stand facing the anchor point with the band taut—and perform the move.