In 1956, 19-year old Kazuhiko Nakadaiji won the Mr. Japan title in a nationwide contest. Greatly impressed with his development, Tokyo police Chief Katsuki Takayanagi hired Nakadaiji to help train his officers and help to build strength for judo. Barbells were limited but calisthenics and bodyweight movements offered a way to allow a large group of people to train at once. Elevated pushups are also, of course,  just as effective today as they are back then and a fine addition to any program.