The sit-up is a strength training exercise commonly performed with the aim of strengthening the abdominal muscles and hip flexors. 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 vertebra from the floor until everything superior to the buttocks is not touching the ground. Stuart McGill of the University of Waterloo has found that situps can be dangerous due to high compressive lumbar load. He suggests replacing it with the curl-up in exercise programs.

Criticism

Although still common in military training, martial arts, and mass exercise classes, the conventional sit-up is sometimes considered dangerous by modern experts, and has largely been replaced by the crunch, since the publication of a research paper on the subject in 1999, for the following reasons: