As one can imagine from the title I will use a tennis ball for today’s exercise, which is great to strengthen the abdominals, the hips and the back muscles.
I lay on my back with bend knees and slightly straddled legs. Now I grab my left knee and pull it backwards until I can pinch the ball between my left thigh and my belly. In this position I start to lift my hips upwards as high as possible and then I lower it back down. After a few repetitions I change the legs.