4) Fueling - filling the tank

Continuous high carbohydrate fueling, as described in the last post, works very well for runners finishing a 100 mile trail race in 24 hours. It works fairly well for most runners who run 30 hours and not at all for those who take 36 hours. At the marathon and 50K distances, it only works for the very slowest runners, because of the difficulty of consuming large amounts of food while running fast. Runners who cannot circumvent glycogen use then need to find ways to increase their glycogen levels before the race.

In the 1930's, genetic disorders were beginning to be discovered that lead to the storage of massive amounts of muscle glycogen. By 1960, it was seen that glycogen depletion in marathon runners ("hitting the wall") was a limiting factor at this distance and ways were sought to increase storage, as it was obviously possible. Åstrand published the first papers showing that this could be done by depleting muscle glycogen and then supercompensating by ingesting more carbohydrate than usual. Athletes who followed this program had mixed results; many improved their times by 10-20 minutes, some saw no effect and a few had disastrous reactions not unlike the symptoms of the glycogen storage diseases. Many variations of depletion/supercompensation have been tried and each has its adherents; the most popular, because it is the simplest and least unpleasant, is to simply increase the percentage of calories that come from carbohydrate for the three days prior to the race.

The one constant in these protocols is that it is not repeated, but done only the week before the race. In the 1990's, "crash training" as done by the world record-setting Chinese women changed that; because they almost certainly used performance-enhancing drugs, their training has been overlooked. My version of a typical week of crash training has one day of a long hard run without food to deplete slow-twitch muscle fibers, then three days of high mileage (generally twice per day) to keep that level down, with an exhausting interval workout the fourth day to completely deplete the fast-twitch fibers. Immediately after this interval workout, following a protocol from a Western Australia University paper, more than 2000 calories in carbohydrate are consumed as quickly as possible; to this gorging, caffeine is added, as it forces glucose out of the liver and into muscle. This is followed by three days of very easy training, when the glycogen is replaced. This method mimics Åstrand's method, substituting running for diet. It has been shown that it takes three days of depletion before the body makes the first adaptive changes to this perceived glucose starvation, but it is unknown whether this weekly repetition alters that. It is also possible that long-term adaptations would blunt the effect, as one becomes accustomed to it.

Crash training will probably never be popular, because it is difficult and risky, but almost everyone has adapted the idea of tapering training before a race, without considering the biochemistry of why they do it.

If one's training to run a world-class flat 50 mile or 100K race, it is unlikely that one could store enough glycogen before the race to get one through it. It's also unlikely that one could consume carbohydrate fast enough to circumvent it's being used. The standard approach would be to store as much as one can and slow its loss as much as possible and hope that one runs out just as one crosses the finish line. But what if you could avoid carbohydrate and glycogen usage completely? That is the approach of ketosis, which will be covered in the next post.