American decathlete Ashton Eaton says tennis is the major pro sport requiring the most athleticism

Cameron Spencer/Getty When a Native American named Jim Thorpe won the gold medal in the decathlon at the 1912 Summer Olympics in Stockholm, legend has it that King Gustav V of Sweden presented him the medal and said, “You, sir, are the greatest athlete in the world.” "Thanks, king," Thorpe is rumored to have responded. Exactly 100 years later, at the 2012 Olympics in London, Oregon-native Ashton Eaton became the latest in a long line of American Olympians to win the gold medal in the decat...