Heading out the door? Read this article on the new Outside+ app available now on iOS devices for members! Download the app.

Lie faceup with your knees bent 90 degrees and lifted over your hips and your arms extended straight up from your shoulders perpendicular to the floor. Keep your core tight and prevent your back from arching as you simultaneously lower your right arm and extend your left leg out straight, then return to the start. Continue, alternating sides.