Forget what your fifth-grade gym teacher told you. Full sit-ups – where you lift your torso all the way up so your elbows touch your bent knees – are "way outdated," says Renderer. Crunches are much more effective. "You just need to curl your trunk so you're raising your shoulder blades off the ground," Bryant says. "The rectus abdominis muscle has a short range of motion, so all that extra movement in a sit-up doesn't engage it any further. Crunches focus contraction where it is most maximized."
Credit: Getty Images
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