How long can I go before refuelling with carbs?

Researchers have been arguing for years about whether carbohydrates make any difference during exercise lasting an hour or two and, if so, how much you need. Recent experiments suggest that during shorter workouts, carbs are for the brain rather than the muscles, and that during longer workouts, not all carbs are created equal.

http://www.theglobeandmail.com/life/health/alex-hutchinson/how-long-can-i-go-before-refuelling-with-carbs/article1878842/