TRX Pike

Your feet are suspended in the straps, which demands your core locks down tight from start to finish. Begin in a plank position with the straps at shin height and your body straight. Pike your hips up toward the ceiling, pulling your feet closer to your hands, then lower back to plank. The straps will move; your body must not. This constant fight for stability is the entire point — your core cannot relax for even a second.