Leg raises. This is a classic exercise for the large abdominal muscles, which, unlike knee raises, works the lower abdominal muscles with fully extended leg raises. Also, the body remains motionless throughout the exercise.

There are several options for doing this exercise. However, there are two popular ones. The first is performed lying on the floor, the second – on a horizontal bench. The execution technique for each of the cases is almost identical – the legs from the starting position (parallel to the floor) rise upwards with a smooth movement (perpendicular to the floor), the hands play only a stabilizing role. In the case of lifting on a horizontal bench (this can be a bench press), the legs in the starting position fall below parallel with the floor in order to further increase the range of motion and stretch the abdominal muscles more. As with other leg raises, weights can be used to increase the load.
Keep your body straight and keep your back straight.
Lie on your back with your hands under your buttocks.
Keep your lower back off the floor.
Fully extend your legs and keep them straight.
Raise your legs up perpendicular to the floor.
Lower your legs to the starting position, but do not let your feet touch the floor.
All movements should be performed by the abdominal muscles and hip flexors, do not help yourself by swinging your legs.