Why: Targets your abs, obliques, low back and even your hip flexors.
How: Assume a push-up position with your body in a straight line. Flex your right hip and touch your right knee to your left elbow. Extend your leg behind your body to return to the starting position. Repeat on the opposite side and continue in alternating fashion for the specified number of reps.
Sets/Reps: 2×5 each side
Photo Credit: Getty Images // Thinkstock