How to do the bent over dumbbell row back exercise doing one arm, one side at a time:
Find a flat bench and place a dumbbell by the right side of the bench. If this is your first time doing this exercise, I recommend that you begin with very light weights to get a feel for the movement and proper balance.
Your left right arm and hand will be placed on the bench and your left knee is also placed on the bench to give you support on your left side while the opposing right leg is pressed against the floor and a little outwards. Your back will be flat but not perpendicular to the bench – a little more than 45 degrees from the angle of the bench. It basically follows the linear progression of you leaning your arm/hand against the bench and your knee against the bench.
Grab a dumbbell with your right hand using a parallel grip and pull it up to your rib cage/torso. Make sure to keep your elbow close to your side. You don’t want your elbows flying outwards, then the movement would be all wrong.
Slowly lower the dumbbell in a slightly forward motion until your arm is more-or-less straight except for a slight bend in your elbow.
Repeat the movement for about 8 to 12 repetitions.
Do the same for your left arm.
Do about 4 to 5 sets of this exercise.