The plank is an isometric core strength exercise that involves maintaining a position similar to a push-up for the maximum possible time. In this variation, while in the plank position, one arm at a time shift from a 90 degree angle to a fully extended arm pushing away from the ground. Reverse movement to complete exercise.

1. Start in a plank position with your hands directly under your shoulders and your body in a straight line.
2. Lift your right hand and tap your left shoulder.
3. Return your right hand to the starting position.
4. Lift your left hand and tap your right shoulder.
5. Return your left hand to the starting position.
6. Continue alternating taps while maintaining a strong plank position.