The leg curl is a classic hamstring exercise. The medicine ball version of the leg curl is slightly different because it requires an element of skill. The med ball is positioned between the shoes via muscular tension. The inner thigh muscles (adductors) allow this to take place. But on the classic leg curl exercise, the inner thigh muscles are not recruited.

To begin, lie face down on the floor. This exercise can also be performed on a flat weight bench. Next, secure the med ball between the shoes. Curl the legs to a 90 degree angle and return to the starting point. Keep the butt flat during this exercise.

It is important to note that the weight of the med ball is only effective until approximately 45 degrees. As the ball travels past 45 degrees, there is less weight acting against gravity. So at 90 degrees, your bone structure is actually supporting the weight with leverage. There is no muscle involvement at this point.