Begin in the up position of a push-up: arms extended, back and neck in a straight line, and core tight. This will be your starting position.
Descend into the bottom position of the push-up by flexing at the elbows into a 90-degree position.
Lean (and shift your body weight) to one side by attempting to place your front deltoid on your palm. Simultaneously, extend your opposite arm into a straight line. Your bent arm may move slightly to accommodate your other arm fully extending. This is okay.
Next, transition your weight to your opposite arm, repeating the same motions. Once completed, this is one repetition.
Rock back and forth, and repeat for recommended number of repetitions.