The last event to happen among the options listed is Title IX forbids gender discrimination in sports.
Title IX was enacted in 1972, whereas the other events happened earlier:
- The YMCA was founded in 1844, and the first gym opened in the U.S. in the 1850s.
- Physical education (PE) became part of American school curricula around the late 19th and early 20th centuries.
- The adjustable plate-loaded barbell was invented in the 20th century but specifically during the mid-1900s.
Thus, Title IX (1972) is the most recent event.