The abdominal exercise where you raise your upper body from lying flat to a sitting position is called a sit-up.
A traditional sit-up begins with the person lying on their back, usually with the knees bent and the feet on the floor. The upper body is then lifted until the torso rises well clear of the ground, before returning to the starting position. The exercise involves the rectus abdominis and also recruits the internal and external obliques and hip-flexor muscles.
A sit-up is not the same as a crunch. A crunch uses a shorter range of motion, lifting only the upper back and shoulders, while a sit-up raises the torso much farther. A bridge and a plank are also abdominal exercises, but they rely on different movement patterns and do not involve repeatedly sitting up from the floor.
Sit-ups have been used in physical-fitness testing and military training, but concerns about lower-back stress have led some programs to favor planks and other core exercises. Weighted, incline, and arms-crossed versions change the difficulty without changing the exercise’s basic identity.