Popular entertainment is often powered by schadenfreude. In Roman times, spectators packed stadiums to gleefully observe as people were dismembered by lions. More recently, the explosion of reality television has given popcorn-munchers the chance to watch people make themselves sick from eating too many cockroaches or undergo extreme plastic surgery to look like flash-in-the-pan celebrities. 

Depression-era dance marathons are the 1930s counterpart to 2000s reality television. These spectacles began innocently enough as dance contests in the 1920s, when long-haul dance events trod the fine, fascinating line between sexily scandalous and over-the-top outrageous. Alma Cummings kick-started the craze in 1923, wearing holes in her shoes from 27 straight hours of dancing in a Manhattan ball...