The Double Bend And The Windshield Wiper.  No, this isn't the title of a book, it relates to two basic but crucial concepts of the modern forehand.  Incorporate them into your own forehand groundstrokes and you'll see your game improve remarkably.

What's the double bend?  This is the position your arm should assume when you have completed your backswing.  Whether you take your racquet back with a big loop or a more abbreviated straight back backswing, at the end of the backswing your elbow is bent and your wrist is laid back.  The head of the racquet is pointing toward the back fence, and the butt of the racquet is pointing toward the ball.  Once this double bend is achieved, it is maintained throughout the forward swing and far into the follow-through. 

Check out the slow motion videos on VJTTA.com of Andre Agassi or Roger Federer and others.  You will see a wide variety of backswings, but they all end in the same double bend position. 

Why is this double bend position important?  A bent elbow will provide leverage as the racquet makes contact and lifts the ball.   Just as you always bend your elbows when you lift heavy objects, the same is occurring when you contact and lift the ball.  While the amount of bend in the elbow will vary, it is seldom straight.

The flex in the wrist helps set the racquet at the end of the backswing so it is on edge, perpendicular to the net, and ready to move forward and be parallel to the net at contact.   Since most balls are hit out in front with most of your palm behind the racquet handle, a bent wrist again provides maximum leverage on the ball as the racquet swings up and through the shot.

The modern forehand is almost all about leverage, which the double bend position maximizes.  Unlike the more traditional swing path, today's forehand can be characterized as a brushing up and across the ball.  The racquet head's swing path resembles a windshield wiper action, as if the ball is being turned up and over the net.  The double bend position maximizes the efficiency of this stroking action.

You can get a good feel for this double bend by doing this little exercise at the net. Stand sideways a few feet away from the net with the net near your left hip.   Take your racquet back so that it is perpendicular to the net, but with your elbow bent and your wrist laid back.  Now lock your wrist and slowly rotate your hitting shoulder back toward the net.  Strike the net cord gently such that half of your racquet face extends above the net. Continue to push the racquet face against the net with your hitting arm, building resistance as your weight shifts forward against the net.

Now raise your hitting arm slowly upward until your racquet is free of the net.  As the lower edge of your racquet clears the net cord, allow your hitting shoulder to come forward as you  use your hitting arm to both hit out and hit up on the imaginary ball.

This hitting up and hitting out action, combined with a rotating shoulder, will give you the windshield wiper action on the ball.   Note that if you have a conservative grip (such as the Eastern Grip or Modified Semi-Western Grip) your hitting shoulder will stop moving forward once it gets about parallel with the net.  If your grip is a Moderate Semi-Western or an Extreme Semi-Western, your shoulder may turn forward more, until it ends almost perpendicular with the net.  This is a function of the grip and the need for more extreme grips to make contact with the ball farther in front of the body.