This exercise is a convenient alternative to the traditional barbell row. The main target is the upper back, or scientifically, the latissimus dorsi. The "lat" muscles function to pull things. So whenever you open a door, your lat muscles are allowing the movement to take place.
Begin by securing the resistance tubing under your shoes. Ensure that the tubing line is fairly tight. The goal is to ensure that there is plenty of resistance throughout the entire range of motion.
Bend over so that your back is approximately 45 degrees. Be sure to maintain a straight back, as it will ensure proper spinal alignment. Bend your knees slightly, then pull the resistance tube into your abdomen area. Your elbows should remain close to your rib cage as you pull. Slowly lower the tubing and repeat the exercises as desired.
IMPORTANT: Never round your lower back. This is bad for the spine.
Grasp tubing handles. Bend 45 degrees.
Pull tubing into abdomen area. Keep elbows in.
Return to start position. Repeat.