As the U.S. military processed several million enlistees and draftees into the armed forces in 1917 and 1918, it became clear that American men were not in great shape. They weren't even in good shape.
The poor condition of the incoming servicemen impacted the training in the military camps but also had an effect post-war when efforts began to promote physical health in the general populace. This affected American universities in two ways. One was adding physical education requirements for most students, and the second was to initiate intramural athletic programs. Before the war, schools commonly had interclass competitions, but the intramural programs aimed for much wider participation.
A related line of thinking impacted college football when Michigan President C. C. Little made a 1926 proposal for schools to allow more students to participate in varsity competitions. Many state universities had become large enough that their student bodies included excellent athletes who could not make the varsity team but could play on a second team. The proposal went nowhere in 1926 but gained the approval of Big Ten athletic directors and faculty members in 1927. The ultimate vision was for each Big Ten school to field two teams, with the first and second teams playing home and away games each weekend.