Outside, it’s a few degrees south of zero. But inside this CrossFit gym in Grand Forks, N.D., a half-dozen fitness nuts–three men, three women–are just warming up. Tom Harmon, a former Army reservist ...

Over the last decade, CrossFit has grown into one of the hottest fitness trends in the world, with over 14,000 CrossFit gyms – known as ‘boxes’ – springing up across the globe. Its many passionate ...