Major Muscles and Actions Involved

The upper rectus abdominis and internal and external obliques are involved in spinal flexion. The upper rectus abdominis is not a separate group of muscles; rather, only the upper portion of the entire muscle is in action, as substantiated by EMG (electromyographic) studies. The rest of the muscle remains under tension. In this exercise your head and shoulders are lifted and move toward your hips. 

Sports Uses

The sit-up exercise is important for all athletes who throw implements with maximum force (baseball, football, javelin, shot) and for those who perform acrobatic type movements such as diving, trampolining, and gymnastics. Upper abdominal development is very important to bodybuilders because these muscles show the ripped effect. Athletes who must handle heavy loads or must stabilize their spines, need strong abdominal (and lower back) muscles to maintain firm midsections. 

Did you know...

• There is considerable controversy over whether your legs should be straight or bent at the knees when you do the sit-up. In general, your knees should always be bent when your legs are held down or secured in some other way. When you attempt to do a sit-up with your legs straight, the psoas muscle (which is a hip joint flexor and is attached to the lower vertebrae) comes into play. This muscle can cause the lower spine to hyperextend (arch) if the abdominals are too weak, which in turn can cause lower back problems if the stress is sufficiently great.