The third step of the one-handed backhand is to use your arms, as well as a continued shoulder turn, to get the tennis racket all the way back and your shoulders completely sideways.
In the video above, once I pivot and turn my shoulders I use my arms AND my shoulders to get the tennis racket back and my shoulders sideways. At about 25 seconds into the video we watch the entire motion up to this point. Coming out of the split step, the pivot and shoulder turn starts the racket take back. When I complete that initial step, then my arms help me get the racket all the way back. We’ve highlighted this fact a number of times here and in other sections because it’s so important to hitting not only a correct one-handed backhand, but also any other groundstroke in the game.
At 50 seconds into the video we watch Andrej hit his split step and begin to hit a one-handed backhand. He pivots and turns his shoulders. Because his shoulders are turning sideways the tennis racket starts to come back. Once he has completed this step, he uses his arms, as well as a continued shoulder turn, to get the racket all the way back.