Santa Monica-based LIVESTRONG.COM, the fitness and healthy living site run by Demand Media, said this morning that it has seen a "momentous activity spike" in usage of the site. Livestrong.com said it had over 12 million unique visitors in January 2011, an all-time traffic high for the site. Livestrong said the numbers place it as the largest, single website in the United States in the health category, according to comScore. Livestrong.com is a joint venture of Demand Media and Lance Armstrong.