Start on your hands and knees, shoulders directly over wrists and hips over knees, holding a dumbbell against the ground in each hand. Brace your core and extend your legs back behind you, tucking your toes under to lift your knees off the ground and spreading your feet wider than shoulder-width apart. This wide-legged high plank is your starting position. (You can modify by placing your hands on an elevated surface, like a bench, couch, or sturdy chair.)
Pull your core toward your spine and squeeze your glutes as you lift the right dumbbell off the ground, pulling it to your right armpit. Make sure your right elbow is pointing up and your right shoulder blade is squeezing in.
Lower the weight to the ground with control, bracing your core and glutes and doing your best to minimize any rocking movement from side to side.
This counts as one rep. Repeat for 10 reps with your right arm, then switch for 10 reps with your left arm.