So far in this series of posts, I've talked only about food and I want to transition to exercise. The one place where the two clearly overlap is the process of carbohydrate loading. I've discussed it before, so much of this is repetition.
When I first started running, everyone talked about "hitting the wall" in the marathon and carboloading, but now it's rarely talked about. Part of the reason is that, when I ran my first marathon, the average finish time was 3:40 (and only 10% of finishers were women) and they shut the clocks off at 4:30; today 4:30 is better than average. If one runs slowly enough, one doesn't run out of muscle glycogen, which is what hitting the wall is all about, so it's only a concern for those who are trying to run the distance as fast as they possibly can, rather than to finish comfortably or just finish. The first major proponent of carboloading was Ron Hill, who found that his finish times with it were 2:12-2:15 and without it 2:20-2:25; if he didn't tailor his diet for the race, he involuntarily slowed to his usual training pace around mile 20 (still 6 minutes per mile) or slowed dramatically with 3 miles left (about 7 minutes per mile). Most people aren't worried about 7 minutes in a marathon, so they don't bother.
Muscles store carbohydrates in the form of glycogen, which cannot be restored during the time of a race. Typically, average runners have enough glycogen stored to last about 13-17 miles, those who have trained for a marathon slightly more, but not enough for 26 miles; they are able to finish the marathon, however, because glycogen is not the sole fuel used in running (in fact, the majority is fat, regardless of pace, beyond 30 minutes of exercise).
Gunvar Ahlborg in the 1960's experimented with the idea that one could cause muscles to store more carbohydrate than usual. The idea was that, if one depleted muscles of glycogen, the cellular machinery would go into overdrive trying to scavenge as much carbohydrate as they could. Then one would flood the body with carbohydrate and the glycogen stores would build dramatically before the body recognized that there was no longer a shortage. This would only work because, once glycogen is stored in muscle it can only be used by that muscle during exercise (liver glycogen can be used for energy anywhere it is needed); it is trapped. His plan was to have runners deplete their muscles with a long run, then eat a diet low in carbohydrates for three days to ensure depletion, then eat a very high carbohydrate diet for three days. The procedure worked; runners were able to store as much as three times as much glycogen this way.
This was the standard for about a decade, when others started to question whether it was the best way - or only way - to achieve these results. Many runners found that the low carb diet made them irritable and lethargic and they abandoned that part of the plan with no adverse effects. Later experiments found that the amount of improvement in glycogen storage differed dramatically among runners and that the original procedure worked best for those who were not trained athletes; it appeared that well-trained runners depleted as well during those three days by running as they would by a low carb diet.
The biggest change in thinking about carbohydrate loading came from a study in 2002 at Western Australia University. They found that one could double glycogen stores in one day. The method was to run about 1 mile pace for 2-3 minutes, then follow that with an all-out sprint and then consume huge amounts of carbohydrate (mostly liquid) within 2-5 hours. This method has some distinct advantages, but is uncomfortable to follow - in trying it, I found myself ingesting a gallon of water containing 10 ounces of corn syrup while eating an entire angel food cake in two hours, then not feeling well again until the next morning.
There are multiple ways to deplete muscles of glycogen, because muscles are made of more than one type of cell. One sure way is to run a race; instead of a long run at the beginning of the Ahlborg method, one could run faster for a shorter distance - the problem being that a 10 mile race the week before a marathon would not allow enough time for recovery (unless, perhaps, one runs 120+ miles per week). A long race or a very long stamina run will deplete the glycogen of slow-twitch muscle fibers, but not necessarily the fast twitch fibers. A sprint will deplete the Type B fast twitch fibers, but no others. A very fast run to exhaustion as in the WAU procedure, depletes mostly the Type A fast twitch fibers.
Combining these methods, one could conceivably get better results. The procedure I came up with is to do a fast tempo run one day and follow that with a very long stamina run, then a couple of days of moderately heavy training (by running twice a day) including hills and short sprints, then a day of hard intervals, followed by three days off to recover. I wouldn't eat during the long runs which averaged 5 hours and would stuff myself with carbs immediately after the interval workout. While I feel the method worked as an experiment, it involved too much hard work too close to a race and the stored carbohydrate also meant excess stored water weight. While I had the energy stored to run fast for a long way, much of it was stored in muscle fibers not utilized in the race itself.
In ultramarathoning, the idea is to run without tapping into one's glycogen reserves (until very late in the race or on a long uphill). The standard method is to intentionally run slowly enough that this is not an issue and to improve one's times by gradually becoming more comfortable with slightly faster paces. This works well for true ultrarunners, whose muscles are made almost entirely of slow-twitch fibers, but for most runners, including me, half (or more) of their muscle fibers are not being used; they are essentially running on one leg. They have to learn how to use the fibers they have to achieve the same results.
