Football is one of the most popular sports in the world, with an estimated 240 million (in 2000) 1 to 265 million (in 2006) players
participating in the game. The sport involves intermittent walking, jogging, running and sprinting, and has a higher incidence of injuries than rugby, volleyball, field hockey, cycling, boxing,
swimming and basketball. In 2001 it was reported to have injury rates of 1 000 times higher than for industrial occupations generally regarded as high risk. Due to the biomechanical factors inherent in football and it being classified a contact-collision sport, the knee is exposed to both intrinsic and extrinsic forces that make it highly susceptible to injury. Ball size, shoe wear, protective equipment, and playing surface conditions are all mechanical factors that can be potentially modified if implicated in injuries. However, individual playing styles and techniques are less easily controlled.