Start by standing tall with your feet at shoulder-width apart.
Explosively drive your right knee up toward your chest as you bring your left elbow forward.
Quickly switch sides, bringing your right foot down and driving your left knee up.
Alternate side as quickly as possible, using the momentum from your arms to drive your legs high.
2. Hollow Hold
Lie on your back with your arms extended overhead and legs out straight.
Using your core, lift your head, shoulder blades and legs off the ground. Keep your biceps by your ears and actively press your lower back into the ground to ensure you're engaging your abs throughout the entire exercise.