Forget that version of the situp you performed in grade school (the one in which you jerked your neck up like someone had just blown an air horn next to your ear). Instead, embrace the classic situp, and follow these guidelines on how to do it correctly from Nate Green, a trainer in Whitefish, Mont.
1 LIE ON YOUR BACK ON THE FLOOR, BEND YOUR KNEES 90 DEGREES, and plant your feet flat. Tuck your chin slightly toward your chest. Raise your arms off the floor so that they’re parallel to your body and pointing toward your feet.
2 KEEPING YOUR FEET AND BUTT ON THE FLOOR, RAISE YOUR TORSO OFF THE FLOOR and toward your thighs, coming up as far as you can (it’s OK to let your lower back come off the floor). The movement should be smooth; don’t jerk. Reverse the motion to return to the starting position. That’s one rep.
Correct these common problems for better situp form
YOU DON’T GO HIGH ENOUGH. Years of doing crunches may have taught you to raise only your head and shoulders off the floor. Nonsense. “Allow your lower back to round as you come up,” says Green.
YOU PULL YOURSELF UP BY YOUR NECK. It’s OK to place your hands behind your head, but don’t pull your head forward as you rise; it causes neck strain. “Start by pointing your arms straight forward [as shown at left],” says Green, “then you can progress to folding your arms across your chest, and then to cupping your hands around your ears.”