Leg Raises

Lie on the end of a flat bench or the floor and stabilize your body by gripping the bench above your head or pressing your palms firmly against the ground; extend your legs out.
 
With your legs in a fixed, slightly bent position throughout the movement, raise them up in a semicircular arc until they are about 75 degrees above the level of the floor.
 
Reverse the movement and return to the starting point.
 
The entire motion should be done in a smooth, controlled manner that lasts about 4 seconds, with the downward movement no faster than the upward.