Well the circular motion is more for getting topspin
. Your back and forward motion might be for just hitting flat shots or when you are pushed for time. I dono
The 'C' backswing is not for topspin. You get topspin by swinging low to high, which can be achieved by any backswing so long as you drop the racquet head below the level of the ball before contact and swing up.
The 'C' loop backswing is to aid timing of your strokes. You see it in forehands and backhands.
Here it is in a backhand: Fernando Gonzalez slow mo 1 handed backhand
The common factors in these forehands (and all good forehands) are
1. The Unit turn.
Roddick and Federer have already completed it when their clips start, but you can see Novak performing it in his video (which is why I put it first).
After he split-steps, he uses his left hand to turn the racquet to the right grip while outstretching the left hand and turning his shoulders. His feet are also going to be set up here as well (whether open or neutral stance; the feet set is is VERY IMPORTANT).
Pics of complete unit turns:
THe unit turn is VERY important because it sets you up to begin the stroke. What you can't tell from the pics, is that their FEET ARE LOADED.
What that means is your body weight is loaded/placed on your back foot (right foot for righties).
This is important for the kinetic chain in your SWING to occur properly because your stroke starts from your feet.
2. WEIGHT TRANSFER
After loading the back foot, you start your swing by moving your weight forward. You will end your stroke on your front foot (left foot for righties). THis is important as you don't want to have your weight falling back when you hit the ball. This opens the racquet face and your ball will fly.
3. FIRM WRIST AT CONTACT
Regardless of grip, you want to have a firm wrist atcontact
. For different styles, you may be more wristy or less before and after contact, but at contact that wrist is laid back and FIRM. Moving it will lead to shanking.
That's pretty much it. Everything else is subjective. You can finish over your shoulder or by your waist, hit with more or less spin, more open stance or closed stance; FIND WHAT WORKS FOR YOU!
ALso hit through the ball. No premature pulling up.