the Nevada Athletic Commission, California State Athletic Commission, New York State Athletic Commission and New Jersey State Athletic Control Board. Although these commissions only have jurisdiction over their own states, the Full Faith and Credit Clause of the U.S. Constitution is often interpreted as forcing all other states to recognize any state athletic commission's rulings regarding an athlete's fitness for participating in a sport. Sports media in the United States Sports have been a major part of American broadcasting since the early days of radio. Today, television networks and radio networks pay millions (sometimes billions) of dollars for the rights to broadcast sporting events. Contracts between leagues and broadcasters stipulate how often games must be interrupted for commercials. Because of all of the advertisements, broadcasting contracts are very lucrative and account for the biggest chunk of major professional teams' revenues. Broadcasters also covet the television contracts for the major sports leagues (especially in the case of the NFL) in order to amplify their ability to promote their programming to the audience, especially young and middle-aged adult males. The advent of cable and satellite television has greatly expanded sports offerings on American TV. ESPN, the first all-sports cable network in the U.S., went on the air in 1979. It has been followed by several sister networks and competitors. Some sports television networks are national, such as CBS Sports Network, Fox Sports 1 and NBC Sports Network, whereas others are regional, such as NBC Sports Regional Networks, Fox Sports Networks and Spectrum Sports. General entertainment channels like TBS, TNT, and USA Network also air sports events. Some sports leagues have their own sports networks, such as NFL Network, MLB Network, NBA TV, NHL Network, Big Ten Network, Pac-12 Network and SEC Network. Some sports teams run their own television networks as well. Sports are also widely broadcast at the local level, ranging from college and professional sports down to (on some smaller stations) recreational and youth leagues. Internet radio has allowed these broadcasts to reach a worldwide audience. Most popular sports in the United States In the broadest definition of sports—physical recreation of all sorts—the four most popular sports among the general population of the United States are exercise walking (90 million), exercising with equipment (53 million), swimming (52 million) and camping (47 million). The most popular competitive sport (and fifth most popular recreational sport) is bowling (43 million). Other most popular