Start on your hands and knees on the floor. Walk your hands forward until you're in a knee plank position, hands directly under your shoulders and body forming a straight line from shoulders to knees. Lift your feet off the floor, crossing at your ankles. (If that's not comfortable, leave your toes on the floor.) This is your starting position.
Inhale and bend your elbows out to the sides so they're at about a 45-degree angle from your body, lowering your chest toward the floor.
Pause when your elbows are bent at about 90 degrees, then exhale and push your chest away from the floor to return to the starting position. That's one rep.
Do eight reps. Do three rounds total, alternating with Exercise 1 in this superset.