The next time you are at the gym without a lot of time try this total abdominal exercise:
Set-up
Lay on your back on top of a foam roller. The length of the roller along your spine. Reach your right arm overhead and left arm out to the side. Both legs should be extended with feet resting on the floor about 3.5 feet apart.
The Exercise
Simultaneously reach your right hand and left leg up towards the ceiling crunching the upper body up as you try and touch your ankle. Then lower all the way back down to start position. Make sure not to use your left hand to crunch up. This ensures the focus of the exercise stays in the abs. Repeat the same movement on the same side for 20 reps and then repeat on the other side.
The Benefit
This is a great core exercise. It uses your obliques, quadratus lumborum, rectus abdominus, hip flexors and deep neck flexors. Not only does it flatten the abs and strengthen your back but it also works on your stability since you have to balance on the foam roller.
Added Touch
After you finish both sides, open your arms out wide (palms facing up) and feel your chest open and your back release. This is a great resting position for those that spend most of their days sitting in front of a computer.