The Tac-Tic Knee Trainer is one of the most industry-changing training tools to come along in years. If you coach tennis, you know how many thousands of times each year you tell students the common instruction: bend your knees! The Tac Tic Knee Trainer guides players to bend their knees automatically! They feel and hear a loud click exactly at the moment they bend, whether it is for general balance and movement, to load up before hitting a serve or groundstroke, or to get down for all low balls. Simply put, if the Tac Tic Knee Trainer clicks at the right moment or remains clicked as needed, the right technique is in place. Each unit includes detailed photo instructions. Great for a variety of different sports including baseball, football and basketball.