Effective Situp Positions

Situps provide a convenient way to tone and develop your abdominal muscles, especially the transverse and rectus abdominus muscles. Defining the latter helps you achieve the much-coveted "six pack abs." Situps also target the hip flexors and a muscle called the rectus femoris of the quadriceps. While doing situps alone will not give you a "six pack," they will improve your core strength without the necessity for any special equipment.
Working the Abs
Step 1
Lie on your back. Bend your knees and place your feet flat on the floor or mat. Position your heels about a foot, to a foot-and-a-half, in front of your tailbone. Place your hands behind your head or cross them on your chest.
Step 2
Squeeze your shoulder blades together. Exhale, tighten your abs and relax your neck. Keep your head in line with your spine, but allow your head and chin to move forward a little bit as you curl up toward your bent knees.
Step 3
Keep the bottom of your feet, your lower back and your tailbone flat against the floor throughout the exercise. Curl toward your thighs only until your upper back is off the mat. Pause for a count of two.
Step 4
Breathe out. Slowly, and with control, lower yourself until your upper back is in contact with the floor. Repeat until you have reached your goal, or until you feel a burning sensation in your abdominal muscles.
Concerns
Curl your body up so your abs approach your thighs and your rib cage moves closer to your pelvis. If you have trouble doing a regular situp, extend your arms in front of you. For a greater challenge, perform situps on a slant board, with your feet higher than your head.
Maintain proper form to prevent stressing your lower back. Don't do the exercise so quickly that you can't keep you abs tight, your shoulder blades together and your head and neck relaxed, but aligned with your spine.