[Ronin]

Wolf, et al.,

One thing that is known, and was recently reported in the health section of the NY Times, is that most people over-estimate their caloric expenditure during exercise.

While I am sure that you are buring calories, you may be over-estimating your actual caloric need -- I know that I was for a very long time. A generally fit person doesn't need an unusual amount of calories for expenditures up to 90 minutes, a truly fit person goes even longer because that person is more efficient in caloric use. As a cyclist I always hear about the 6000 calorie days that is touted as what professional riders consume -- true, but that means six plus hours of racing with an average speed of 25+ MPH, including some rather nasty climbs. Most of us don't come close to that, and even if my effort was close to theirs, my daily routine would probably only consume 1000 calories at most and probably less.

That being said, some carbs prior to exercise is a good idea as this is quick energy. Generally speaking you will have sufficient stored glycogen in your muscles and liver to keep you going for the times you mentioned. And, your post exercise BG levels can actually go up if you get a liver-dump as a result of exercise.