Burpees
More of a cardio exercise than a core exercise burpees will get your heart racing. For the majority of people I’ve found performing burpees using blocks or books allows for much smoother movement, reduced impact forces and better biomechanics without sacrificing cardio benefits. Starting in a push up position. Jump your feet forwards between your hands. Perform a small vertical jump before reaching back down and jump your feet back to the start position. You should aim to move as quickly and quietly as possible. To reduce the impact of the exercise eliminate the jumping portion of the move!