Start by using 2 boxes or benches at equal height or close to equal, sitting at the edge of your box hands palm down shoulder width apart on either sides of your hips; grip the edge and the bottom of your heels dug into the box/bench across from you toes pointed upward.
Extend your arms while lifting your bottom off the box and lowering yourself down right in front of the box, until you reach a 90 degree angle with your elbow flexion. Pressing back into extensions and repeat.
Going directly into Plank taps.  Straight arm plank; palms placed directly under your shoulders perpendicular to the ground. Without swaying back and forth, pick up each side and taping your opposite shoulder and placing your palm back on the floor. Its important that your core is tight throughout this exercise and you stay in a perfect straight arm plank position.

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