The exercise/stability ball roll out looks like a simple exercise, but is surprisingly tough! The exercise is typically performed with a stability or exercise ball, but it is also possible to purchase specific roll out handles which are made for this exercise.
Most gym-goers perform the ball roll out within their core/abdominal training as it is commonly perceived as an abdominal exercise. However, when the exercise is executed there is no notable flexion of the waist; therefore the stimulus to the abdominals and the obliques comes in the form of an isometric contraction (i.e. the rectus abdominis contacts to stabilise the trunk, but the muscle does not shorten or lengthen to any meaningful degree).
While it may be considered an abdominal exercise regardless of the isometric contraction, the dynamic muscles contractions occur mostly to the muscles of the upper back, to flex the shoulder, as well as the hamstrings which aid in the flexion of the knee. We have labelled these as secondary targets on this profile due to the limited stimulus the exercise provides to these muscles, and the fact most people perform the exercise ball roll out for the stimulation it provides to the midsection.