How America's love of watching sports created superhuman athletes

Athletes' bodies are changing— they're faster, stronger, more efficient and are shattering records from decades ago, and it's all thanks to you. As sports became a spectator event in the 20th century, athletics veered away from a leisure activity for the few, to a multi-billion-dollar industry that attracts the best of the best and encourages them to push to the ever higher plateau of physical feats.