Lie on your side with your bottom arm supporting your head or extended along the floor. Reach your top arm overhead and let it drop toward the floor in front of you, rolling your chest slightly open as your ribs stretch along that top side. Keep your hips stacked rather than rolling your top hip forward to compensate — that roll is what actually determines whether the stretch reaches your lat or gets lost in your lower back. You'll feel a long line from your armpit down toward your hip. Let your breathing drive small extra range rather than pulling harder with your arm.