Posted by: Eric (eritson@hotmail.com) on Wed Apr 13 08:41:47 2005

When you biomechanically break down the swing, the "vastus medialis" is where much of the power comes from at the start of the swing. Using force plate analysis, the "vastus medialis" of the rear leg is the muscle that starts and produces the most force during a baseball swing. It drives the body in a 'linear' fashion to go to the ball, the hips to open, and then rotate more forcefully through and off the ball. This is especially true for right-handed hitters.
For a 175-lb. elite hitter, this small muscle on the inside of knee at the base of the quadriceps can produce a force equal to, or more than, five times the players body weight. Why do you see new-generation hitters such as Albert Pujols slightly lifting their back leg off the ground (with the knee coming forward to the baseball) on home-run swings, the muscle essentially throwing foot off the ground?
The back leg is 'forced' off the ground with unimaginable speed and power, much as it is during a "hang clean" in weight-lifting. The hang clean is the ultimate lift for true athletes, and hitters. The back leg driving into the ground, after the hands and body are "loaded", is what starts an extremely powerful and explosive swing.