http://www.carls-sims-3-guide.com/skills/athletic/Take an Athletic Class
You can take Athletic Classes at the gym in town. This is the best way to gain the first level, as going from level 0 to 1 in any skill in the Sims 3 takes a bit longer. The Athletic class will get you that first level very quickly.
Maybe it should say "You can take
an Athletic Class at the
Stadium in town".
Sorry if it's too minor to notice.