Grab a pillow and stand with your feet slightly wider than hip-width apart. Lower into a squat and place the pillow on the floor under your chest (arms are fully extended, fingertips facing out). Shift your weight into your arms, brace your abs in tight, and jump both legs back, landing in a full plank position. Quickly jump your feet back in to your squat poistion. Repeat, jumping from the plank to the squat position, as many times as you can for 1 minute.
Form tip: The pillow provides a little cushion to your wrists, while the slightly unstable surface makes it more challenging for your core muscles. Be sure to keep your shoulders in line with your hands during the entire movement.