Article: Charles "Wag" Bennett, one of the judges at the 1966 competition, was impressed with Schwarzenegger and he offered to coach him. As Schwarzenegger had little money, Bennett invited him to stay in his crowded family home above one of his two gyms in Forest Gate, London, England. Yorton's leg definition had been judged superior, and Schwarzenegger, under a training program devised by Bennett, concentrated on improving the muscle definition and power in his legs. Staying in the East End of London helped Schwarzenegger improve his rudimentary grasp of the English language. Also in 1966, Schwarzenegger had the opportunity to meet childhood idol Reg Park, who became his friend and mentor. The training paid off and, in 1967, Schwarzenegger won the title for the first time, becoming the youngest ever Mr. Universe at the age of 20. He would go on to win the title a further three times. Schwarzenegger then flew back to Munich, training for four to six hours daily, attending business school and working in a health club (Rolf Putziger's gym where he worked and trained from 1966–1968), returning in 1968 to London to win his next Mr. Universe title. He frequently told Roger C. Field, his English coach and friend in Munich at that time, "I'm going to become the greatest actor!"

Question: Which part of his body did Schwarzenegger work to develop with Coach Bennett?
legs