Running for over 90-120 minutes at race pace can totally deplete glycogen stores even if well loaded beforehand. This means your muscles will have to resort to fat or protein for energy. As fat requires oxygen to burn, you will have to slow right down (or walk!), so that sufficient oxygen can reach the muscles. […]

Are carbohydrates of benefit during a race? is a post from: Time-to-Run Nutrition

Time-to-Run Nutrition