You know how I love the multitasking.
This is a great exercise that not only will strengthen your core, but will work your upper and lower body at the same time. Phenomenal.
1. Start in a regular plank position on your elbows.
2. Push yourself up in to a push up position, so your arms are extended.
3. Return back to regular plank position
4. Take your right leg out as far as you can and leave it there. Take your left leg out as far as you can and leave it there. Your legs are in a wide "V" at this point.
5. Return your right leg back to center, followed by your left leg back to center.
This is one full repetition. Repeat this 15 times and you should be feeling it!