If you’ve never worked out with a BOSU ball—it looks like half a yoga ball attached to a solid, flat base—it may be time. In bodyweight exercises, a BOSU ball adds an element of instability and challenges your body to compensate. With the flat side up: Squats, planks, and push-ups train balanced weight distribution. With the round side up: Go for core work, like scissor kicks and bicycle crunches.