Sit-up

The sit-up is a strength training exercise. It begins lying with the back on the floor, and then elevating both the upper and lower spine from the floor until everything superior to the buttocks (bottom) is not touching the ground. This can be performed with resistance. Due to leverage, one's feet can sometimes leave the ground so they are sometimes held by a partner or hooked under an object to prevent this.

The situp can be performed with any variation in leg position as long as it remains consistent throughout the exercise. Straight-legged, or with the knee forming a 90 degree angle with the ground are the most common variations. Advocates have argued for either based upon variations in hip flexor recruitment and lower back stress. A bent knee is useful as the ball of the foot and toes can be dug into the floor as an alternative to hooking feet under an object or requiring a partner's assitance, for people who cannot do it without losing balance. On the other hand, this is generally not required as leverage is more inferior with straight legs.

The hands can be kept in any position, with straightened out parallel to the body being the easiest. Raising the arms above the head will make the exercise more difficult. Flexion of the elbow will make the exercise more difficult up until a point (varying throughout the exercise) where extension will induce more difficult leverage demands.

The exercise works the abdominal muscles and hip flexors. For some with core muscle imbalances, stress is sometimes felt in lower back. Controversy regarding recruitment of the abdominal muscles has caused sit-ups to be replaced by crunches in many places.

Many people do many sit ups each day in an attempt to gain a 'six pack'. Abdominal exercises will not cause hypertrophy beyond a certain point without additional resistance added. Body fat in the abdominal region must be very low in order for the muscles to be very visible, and as such a low calorie diet is often used in conjunction with fat-burning exercises to obtain this. Building muscle will elevate the base metabolism, and aerobic exercise (including progressive cardiovascular conditioning) can burn additional calories, so the diet need not undergo as much restriction. Diet must still be monitored as exercise can increase hunger in some people to negate the effects of additional calorie expenditure.

The sit-up places considerable stress on the lower back vertebrae, so individuals who experience lower back pain can sometimes alleviate this by doing crunches as an alternative abdominal exercise. Some research suggests that sit-ups may do more harm than good to the back [1], though others claim that, if done correctly, they may be beneficial eustress for people who are conditioned enough to perform them without injury, much like resisted isotonic back extension.[2]

The individual should conclude to what weight should be lifted (i.e. anything above the waist) and how much leverage they have to pull against (i.e. everything below the waist).

As abdominal strength increases, the amount to be lifted can be gradually increased by varying these two variables. This is done by moving the position of the arms and legs in relation to the pivot point. To further increase resistance beyond the position of your arms and legs, an external weight may be used. Medicine balls are ideal due to being able to hold it between the hands and easily rest it on the chest, unlike dumbbells. Similar to creating resistance by positioning one's hands, holding the medicine ball further above one's head will increase the resistance.

Some sit-ups are performed in a sideways manner. The purpose of these is to strengthen the Abdominal external oblique muscle, as opposed to the frontal abdominal muscles. To perform these, the person lies on one side, legs together, with their arms in front of their body, hands clasped. Contracting the oblique muscles on the upward-facing side of one's body will pull one's body into a bow shape, similar to the effect of an abdominal crunch.