| I think talking about the energy capacity and calorie loadings of athletes, is not a useful guide for ordinary reasonably fit mortals such as ourselves.
I suspect that Bluesky is perfectly correct in maintaining that an athlete has enough glycogen to supply the body with enough energy for 2+ hours at 85% MHR - and this is borne out by the endurance capacity for professional athetes, and the timing of when non-professional but fit marathon runners "hit the wall."
XC cyclists will complete a course in around 2 hours with a heart rate averaging 170-180. A colleague of mine who ran for Hampshire, and finished regularly in the top 10 vets, and does triathlons. Has a heart rate of around 175 when he runs, and he is able to maintain this level for around 2 and a half hours.
The 45 min figure was not mine, but was pulled from a sports physiology page. And for normal reasonably fit mortals seems to be about right - certainly seems to be about the endurance level that me and mates can achieve whilst mountain biking.
following strenuous exercise where, you have nearly depleted your body's glycogen, and this can occur in a normal reasonably fit individual in around 45min to 1 hour running at 85% MHR. The muscles response is to become much less insulin resistant. They act like a sponge soaking up any spare glucose including whatever glycogen is left in the liver.
The point of a post exercise snack is to maintain glycogen levels in the liver - and as I said, if you are diet only, then this will not matter, you will just feel tired. However, if you are on insulin, failing to replenish glycogen after exercise is risky.
A woman I met on a course experienced exactly this phenomenon. During the day she had exercised hard in a longer than normal gym session. She had then eaten low carb that night - during the night she went into a hypo, and her husband couldn't wake her. The ambulance crew gave her glucagon (standard procedure in these cases), and she failed to respond. When she did not respond to the second dose, they had to put her on IV glucose. Apparently it took an hour for her to regain consciousness.  | 
