7. FROG CRUNCH
This variation will not only challenge your balance and stability, but also target your lower abs and strengthen your entire core. Start seated with your knees bent out in front of you. Lean back slightly so your torso is at a 45-degree angle to the floor and your shins are parallel to the floor. Keep your abs involved as you straighten your legs and simultaneously bring your arms out to the side. Bring your arms and legs back in to the starting position. Continue pulsing like this as you hold your core steady.