Sit-up

It is similar to a curl-up (that targets the rectus abdominis and also works the external and internal obliques), but sit-ups have a fuller range of motion and condition additional muscles.

The knees and toes are bent to reduce stress on the back muscles and spine.

Both the upper and lower vertebrae are elevated from the floor until everything superior to the buttocks is not touching the ground.

argue that sit-ups can be dangerous due to high compressive lumbar load[1][unreliable medical source?]

[11] In 2015, it was revealed that every branch of the U.S. armed forces have begun to phase out sit-ups and crunches, due to the high rates of lower-back injury.