The sit-up is a strength training exercise commonly performed with the aim of strengthening the hip flexors and abdominal muscles. It begins with lying with the back on the floor, typically with the knees bent in an attempt to reduce stress on the back muscles and spine, and then elevating both the upper and lower vertebrae from the floor until everything superior to the buttocks is not touching the ground.

Sit-ups are a basic exercise used in civilian athletic training or physical education and commonly in military physical training.

The Bleep Sit-up Test measures abdominal strength and endurance. In this test, the maximum number of sit-ups performed at a rate of one every three seconds is recorded.