Grab a pair of dumbbells with an overhand grip (or anchor a resistance band) and stand with your feet together. Brace your abs in tight and extend your arms out in front of your chest, palms facing in. Pull your shoulders down and back and keep them there during the entire movement. Bend your left elbow and pull your arm behind you (as if aiming a bow and arrow). Imagine that you're squeezing a lemon between your shoulder blades. Extend your left arm and bend and pull your right arm back. That’s one rep. Repeat 15 times total.