Runners — a group of people accustomed to bloody nipples, blackened toenails and mid-route diarrhea — seem to become embarrassed by only one thing: treadmills. “They say, ‘I can’t get on one.’ There’s this shame,” says David Siik, creator of Equinox’s new Precision Running program. He has plenty of reasons athletes should get over their hang-up: Treadmills are gentler on the joints than unforgiving sidewalks, they allow groups of different abilities to run “together,” and they make it possible for a coach to monitor an athlete for every step of a run.