Begin in a push up position, but with your feet apart (the closer your feet are together, the less stable, and more challenging the exercise will be) Assume PPT (tuck your tailbone) Create total body tension, bracing the core, squeezing the glutes. Grip the floor with your working hand, arm straight, squeeze your armpit.
Lift the other arm off the floor, maintaining your posture. Shoulders and hips stay level, resist rotation. Breathe through the exercise, keeping your core braced. Hold for time and switch arms.
The purpose of this hold is build strength through anti-rotation, the non working arm should be in line with the body, but avoid pressing it into your back or holding your leg as this promotes compensations and is counterproductive to the goal.