The sit-up is a calisthenic abdominal exercise that works the rectus abdominus muscles. It was once considered the gold standard for working the midsection, but fell out of favor due to controversy dealing with lower back injuries. The sit-up is still used by many military personnel as a gauge of abdominal endurance.The sit-ups are dangerous and very difficult to perform.
The situp primarily utilizes the rectus abdominus and the hip flexors, along with a multitude of stabilizers.
According to the US Army, proper form is as follows: "The sit-up event measures the endurance of the abdominal and hip-flexor muscles. On the command "get set," assume the starting position by lying on your back with your knees bent at a 90- degree angle. Your feet may be together or up to 12 inches apart. Another person will hold your ankles with the hands only. No other method of bracing or holding the feet is authorized. The heel is the only part of your foot that must stay in contact with the ground. Your fingers must be interlocked behind your head and the backs of your hands must touch the ground. Your arms and elbows need not touch the ground. On the command "go," begin raising your upper body forward to, or beyond, the vertical position. The vertical position means that the base of your neck is above the base of your spine. After you have reached or surpassed the vertical position, lower your body until the bottom of your shoulder blades touch the ground. Your head, hands, arms, or elbows do not have to touch the ground. At the end of each repetition, the scorer will state the number of sit-ups you have correctly completed. A repetition will not count if you fail to reach the vertical position, fail to keep your fingers interlocked behind your head, arch or bow your back and raise your buttocks off the ground to raise your upper body, or let your knees exceed a 90-degree angle. If a repetition does not count, the scorer will repeat the number of your last correctly performed sit-up. The up position is the only authorized rest position. If you stop and rest in the down (starting) position, the event will be terminated. As long as you make a continuous physical effort to sit up, the event will not be terminated. You may not use your hands or any other means to pull or push yourself up to the up (resting) position or to hold yourself in the rest position. If you do so, your performance in the event will be terminated. Correct performance is important. You will have two minutes to perform as many sit-ups as you can." Taken from FM 21-20
- (1992). FM 21-20 Ch.1, Physical fitness test.. Department of the Army.