It's a bit ironic: More and more Americans are abandoning their couch-loving ways and embracing the outdoors with runs, bikes and hikes. But with races on the rise, their sneakers and wheels are damaging the very environment they so appreciate. Now, some events are launching initiatives to limit impact, and raise awareness among athletes already predisposed to enjoy the scenery. Leading the movement is the Council for Responsible Sport (CRS). Launched in 2007, the organization offers "green" certification to events that pass a six-step evaluation. So far, 25 US races have been certified, and CRS executive director Marisa McGilliard cites a growing trend of road races going green. She anticipates certifying dozens more -- including the Boston Marathon -- within two years.