I'm looking for data on the number of people employed as professional
atheletes (all sports), and reliable estimates of the number of adults
engaged in amateur sports in the USA, UK, and at least one other EU
country (preferably one of the Scandinavian countries). One way to
gauge the number of amateurs might be the number of people belonging
to football clubs and similar, plus those in university or semi-pro
athletics (e.g. national or Olympic teams).  But I'm looking for the
total number of people, not a breakdown by sport.