Kickboxing started in the US during the 1970's when American karate practitioners became frustrated with strict controls on martial arts competitions that didn't allow full contact kicks and punches. Many questions were raised when the sport began about the high risk of injury. As a result, safety rules were improved and protective clothing was added. As this is a relatively new sport there are no long-term traditions. The sport has undergone changes and been refined during the last two decades. Competitors use sparring, kicks, punches, kick blocks, shadow boxing, and wood breaking that is learned and applied under professional instruction.