Start in a high plank position, hands directly under your shoulders. Engage your core and bring your right knee in toward your chest, then quickly switch legs as if one is running.
Stand with your feet shoulder-width apart, holding a weight with both hands. Rotate your torso and bring the weight from one side of your body down toward the opposite knee.
Lie on your back, knees bent, feet flat on the floor. Place your hands behind your head and lift your shoulders off the ground while bringing one knee toward the opposite elbow.
Lie on your back, hands behind your head, and bring your knees up at a 90-degree angle. Alternate touching your elbows to the opposite knee while extending the other leg out straight.
Lie straight on your forearm, keeping your body in a straight line. Engage your core and hold this position, aiming to keep your body in a straight line from head to feet.
Sit on the floor, knees bent, feet flat. Lean back slightly, engage your core, and lift your feet off the ground. Hold a weight or medicine ball (or keep hands clasped together), and twist your torso to touch the weight to the floor on each side.