When you do any type of pulling exercise (this includes all Rows Lat Pulls Etc..), there are two muscle groups which most likely will be involved: Back and Biceps. Most people unknowingly use their Biceps to help or dominate the load of the pull instead of their back muscles. This leaves the back muscles inactive and therefore not working. If your back muscles are not working - they will not change!
Background: The Science of Pulling
Simple Trick: Relax Your Hands!
This tip sounds silly, right? Well, it really works! By relaxing your hands as you pull, you will relax the Biceps and then place all of the pulling responsibility on the Back muscles. My number one choice to help you keep your hands relaxed is to repurpose your ankle straps as wrist straps. By placing the ankle straps around your wrists your hands are literally taken out of the exercise, and they can remain totally relaxed. In the case that you have handles that are permanently attached to your bands, simply grip the bands just tight enough so that they don't fly out of your hands.