Is it muscle which has been specially trained over years of repitition to hitting a tennis ball with maximum force? Technique and the full transfer of energy and use of kinectic force is understandable. Look at this. Murray hitting huge off of tossed balls? I can understand pros hitting hard using the power of one another and timing and technique but I cant understand how they hit so hard and spinny off balls simply dropped like in this video. How? http://http://youtu.be/ZR5VBz8amtgThanks for your replies in advance guys. Any advice on how to achieve such power off dropped balls would be greatly appreciated!!