Plank Hip Twisters
Works: Transverse abdominis, internal and external obliques 
Get into the plank position and lower your right hip to the ground while keeping your feet in place. Try to touch the ground with your hip and come back up to the start. If you can't touch the ground, go as low as possible. Repeat on other side to complete one rep. Continue to alternate sides for 30 to 60 seconds.
More: The One Ab Move You Should Do, But Haven't Tried Yet
Toe-Touch Curl Up
Works: Rectus Abdominis 
Lie on a mat and lift your feet into the air so your hips are hinged at a 90-degree angle. Curl up raising your arms toward your feet. Return to mat to complete one rep. Do this for 30 to 60 seconds.
Medicine Ball Twists
Works: Internal and external obliques 
Sit on a mat with your feet on the floor and a medicine ball in your hands. Lean back until your torso is at a 35- to 45-degree angle. Lift your feet slightly off the ground and rotate your torso to the right, touching the medicine ball the ground. Repeat on the left side to complete one rep. Continue to alternate sides for 30 to 60 seconds.
It's important to keep your core engaged and back straight. If your back starts to curve, place your feet on the ground.
More: Yoga for Weight Loss: 8 Poses to Reach Your Goals
Stay in shape in a fitness class.
