Windshield Wipers is both a strengthening and stretching exercise. Depending on the speed of execution and duration of the exercise it can help you stretch your lateral abdominals and side hip flexors or it can work your lower abs and front hip flexors and even help with lower back and shoulder joint flexibility.
What's involved: Lower abs, front hip flexors, side hip flexors.
Powered by: Lower abs (primarily), side hip flexors.
Tip: You can make this really challenging by increasing the speed but not allowing your feet to touch down every time. This forces you flex your side hip flexors and stop the movement as it completes.