Stand tall, holding one dumbbell in your opposite hand to the working leg (e.g. left hand, right leg planted). Shift your weight onto your standing leg. Slightly bend that knee and engage your core. Keeping your back flat, hinge forward at the hips while extending your back leg straight behind you. Lower the dumbbell towards the floor. Lower until you feel a stretch in your hamstring — your torso and back leg should form a straight line. Drive through your standing heel and squeeze your glute to return to the starting position with control. Complete all reps on one side before switching legs and arms.