Originally Posted by VeeSe
where my knee is 4-5 inches from the ground (that's where all the power came from). .
4" from ground!!! I love to see a photo. I assume you're not small people. The knee bent at 90 deg or less? Your knees won't last long at this bend. Even Sampras has very low bent knee, it still must higher than 12". Bending the knee at this acute angle will not allow the leg drive to accelerate fast, or you must be very light weight. Study the pro serve video, and change yours to save the legs.