Full Sit-up- Lie on your back with your legs straight and your arms extended overhead.  On an exhale, engage your abdominal muscles and sit up tall.  Reach your arms towards the ceiling.  Now slowly and with control lower your torso back down to the ground.  Repeat.

Russian Twist-  Sit with a straight back and your chest open.  Bend your knees and plant your feet on the ground in front of you.  Recline slightly through your torso to challenge your core.  Now begin to twist side to side.  Try to keep the movement short and quick, bringing your hands knee to knee rather than all the way to the floor.  The challenge to your core comes from resisting that rotation in your low back.  Keep breathing and bracing.  Continue for 30 seconds.

Plank Jump- Set up in a tall plank position with your hands directly under your shoulders. Jump your feet in towards your hands, hinging at the hips, and shooting your hips up towards the ceiling.  Immediately jump back into a plank.  Be careful not to let your back sag. Repeat like this for 30 seconds.

Shoulder Tap- Begin in a tall plank with your hands directly under your shoulders and your legs about hip width apart.  Keeping your body steady, lift your right hand and tap your left shoulder.  Now do the same on the other side.  Keep your core engaged and really work to keep your hips square to the ground. Try not to rock.  Continue for 30 seconds.