Footballers' body clocks
This chapter examines the physical fitness of adolescent soccer players and their injuries. The subjects were 56 male players between the ages of 12 and 18 years belonged to a soccer school run by a sports club in Tokyo. Data were collected through a history interview focused on previous injuries, an orthopaedic examination and measures of physical fitness: maximum oxygen uptake, isokinetic muscle strength and speed of joint movement. These results suggest that between the ages of 13 and 14 when knee extension muscle strength increases greatly, to avoid kicking exercises which put pressure on knee joints and instead focus exercise around short distance passing, dribbling, and mini-games. Changes in fitness levels need to be understood and soccer training should be considered according to age. At age 16 years, endurance training started and above ages, sports injuries increased in the players. By performing training adjusted to the different levels of fitness and according to age, these injuries may be decreased.