The Left Arm and Hand Initiate the Stroke
The left arm - or the non-hitting arm - is critical to hitting a big modern forehand. Both Andy Murray and Xavier Malisse are wonderful examples of how the left arm gets set, sweeps in front of the body to initiate the stroke, and finally tucks back at the elbow to really pull the torso around. We like to think of swinging the arm and racket as being the start of the stroke. But that is wrong.
With the modern forehand, the racket and hitting arm don't initiate the stroke. Instead, the left arm starts the stroke and uncoils and pulls the torso around while the hitting arm supinates and then gets pulled by the rotating torso.
Andy Murray has an extreme left arm coil to start the stroke, so he is a great example to see how this works. In the still image above, notice how his left hand is facing the back fence! It's as if he is shaking hands with someone behind him. This creates a wonderful coil in his upper body, and it guarantees that he will use his arms to initiate the swing through an uncoiling motion.
Sweep the Left Arm
In Nick Bollitieri's wonderful "Killer Forehand" video, there is a scene where Malisse is in a pool and he is using his arm to "sweep" the water. In the below animation, imagine Malisse is pushing water with his left arm as he sweeps it around. Next time you are in a pool, this is a great exercise to feel how the left arm should sweep around to initiate the stroke. In the final frame notice how Malisse's left palm is facing the side fence. If you are in a pool, and you sweep the water with your hand and arm, your palm will end up facing the same way.
The Left Elbow Breaks and Pulls Back
After the left arm completes its sweep, the elbow breaks and pulls back. This completes the full 180 degree rotaion of the torso, and it also seems to serve as a breaking mechanism which then accelerates the right side around quickly. By pulling in the left arm at the end, it works like a figure skater that pulls her arms in to increase the rotation of the upper body.
