Beginning in a standard plank, reach left/right arm out in front as far as possible and reach right/lef leg back, pointing your toes down, shooting energy from your heel to the back of the room. Hold for 5 seconds then slowly return arm and leg to floor. Repeat on opposite side.
This move should be performed without rotation or shifting weight through the entire repetition.
For an added challenge, lift opposite leg opposite arm as seen in the picture on the left. For less difficulty, lower down onto your knee, as seen in the picture below on the right.
See video here.