Complex sentence: Griffith Joyner's sudden retirement occurred at age 29, one week after it was announced that random out-of-competition drug testing would be instituted during the 1989 season.
Split into simpler sentences: Griffith Joyner's sudden retirement occurred at age 29, just one week after it was announced that random drug testing would be instituted. Mandatory random out-of-competition drug testing came into effect during the 1989 season.