Last weekend, the Kenyan runners Geoffrey Kirui and Edna Kiplagat won the men's and women's races at the 121st Boston Marathon.
But as recent high-profile cases show, not every athlete is prepared to race within the rules.
Some amateur runners are also resorting to cheating to record a qualifying time and score a prized spot on some of the world's most prestigious races.
Not if Derek Murphy of Marathon Investigation can help it, though. He's a runner and business analyst who's also become a part-time, amateur marathon sleuth as a hobby, using technology to uncover hundreds of suspect times and cheating runners.