At the 151st Kentucky Derby, a global spotlight will shine on equine athleticism. It’s the subject of a growing body of research. On display at Saturday's Derby will be the speed and agility of these 1,000-pound animals. Studies show that a constellation of characteristics are behind the horses' athletic ability. That includes big hearts, immense lung capacity, robust musculoskeletal systems and long, thin legs. All of that helped horses survive in the wild. Experts say it all stems from their evolution as an animal of prey. Horses honed skills like running, jumping and pulling as humans bred and trained them for various purposes over millennia. And the relationship between humans and horses helped shape history.

Bob Baffert is back at the Kentucky Derby for the first time in four years, having served his punishment for Medina Spirit’s failed drug test and coming to the place where he’s won a record-tying six times. He'll saddle Rodriguez and Citizen Bull in the May 3 race. Baffert has his old Churchill Downs barn back and the track restored the signs boasting of his previous Derby triumphs to the wall outside. He says it was a tough three years, but he hasn't let himself become bitter about being banned from the race he values the most.