Following up on this post, I’m going to talk about carb loading the muscles in anticipation of an endurance race. If you haven’t already read the previous post for a basic preview, go read it and come back.
Note that the major source of carbohydrates during exercise is muscle glycogen stores, the greater the stores, the longer you can go before exhaustion. So it would make sense to load the stores to their greatest capacity right? Yes…and No. I’ll get into that in a minute. It’s also difficult to bring these stores above their typical capacity and so it takes a bit of time and effort to bring them to maximum.
There’s a lot of chemistry involved in this. Basically in order to bring glycogen up to the maximum threshold the glycogen stores must first be exercise depleted. Directly after this depletion (seriously hard workout session/run) a person needs to take in 1g/kg of carbs immediately. This should contain some glucose as glucose is best at replenishing muscle glycogen stores post exercise. Squash, oranges, celery, raspberries, and pineapple are all high in glucose. This should be continued every 2 hours for six hours. This is then followed by a training taper (reduction in miles and strength work) as you naturally would in prep for a big endurance race. During the 1st 3 days of this taper, the diet should be 50% carb based. During the 2nd 3 days of this taper, the diet needs to be approximately 80% carbohydrate based.
Basically depleting the glycogen stores causes a biphasic glycogen resynthesis. After the hard workout- and subsequent intake of carbohydrates, muscle glycogen is quickly resynthesized to pre-exercise levels. This takes about 24 hours. It then slowly increases to higher than normal levels over the next few days. This happens because the there is an increase in the muscle’s sensitivity to insulin and the muscle cell membrane permeability to glucose. Research currently points to several days of high carbohydrate intake causing high plasma levels of insulin and that in turn potentially causes a slow phase of glycogen synthase that may be caused by the muscles tissue constantly being exposed to the elevated plasma insulin concentration.
Keep in mind there are other ways to load the muscles. The method I posted has been studied multiple times and included muscle biopsies and so I include it as ‘true.’ Both men and women were included in a decent amount of studies dating back to 1973 (obviously no women in the 1973 study) and a few studies as recently as 2012. If you’re interested in other loading methods, please feel free to ask and I’ll share them. Be aware that some loading methods have been proven dangerous and could cause hyponatremia during a marathon or greater distance, many studies have only been done on young men.
In essence you can double the kcal that your muscles currently hold and now you know how to do it.
Now, what are the cons to doing this?
1) No research can yet confirm how frequently one can do this regimen with the same effect, nor how safe it actually is. Each study is a ‘one trick pony’ so to speak and none say whether there are diminishing returns or damage to any systems in the process (or over time/repeats)
2) By building glycogen stores, weight increases. Glycogen retains extra water. Usually the gain is approximately 2kg (on average) during a carb load cycle with our without the pre-load depletion. For some this would be a con, for others it’s a non-issue.
3) Medical issues. Persons with diabetes or other endocrine disorders, or GI problems need to work with their doctor or dietitian as carb loading is not going to work the same for someone with a medical condition. There are also those that can’t tolerate high fiber diets and high carb tends to equal high fiber if eating complex carbs. Be aware.
4) Not all carbs are equal and eating to abandon is not going to do what one wants it to. Most of the research is pretty split on that one with some saying glucose for muscle glycogen (long-chain glucose polymer solutions are more readily used by exercising muscles) and other studies saying a mixture of glucose and fructose in equal amounts is advantageous.
5) Carb loading is ‘well known’ but difficult to master. The depletion stage is not entirely necessary but the taper stage is vital. Most fail at loading the muscles properly because they don’t taper all the way and don’t take in enough carbohydrate for a long enough period of time.
So what are the Pros of loading up the muscles?
Multiple studies using the carb loading method I listed to increase muscle glycogen concentration to prep for endurance running reported improvements in performance times. There were increases of up to 8 minutes in the Karlsson & Saltin study compared with their performance without loading. *Note that some studies found no performance enhancement at all with loading.
Individuals, who load, should be able to maintain maximal exertion longer. This is of importance to long-distance runners. There is no benefit to loading for distances under 18 miles. Once this endurance distance is reached, the benefits of loading are realized as the extra stores should prevent a decrease in performance that would usually be realized at this point.
Research suggests that pre-race loading (both liver and muscle), combined with hydration and the intake carbohydrates and electrolytes during an ultra-marathon event prevents things like dehydration, hyper and hypothermia, hyponatremia, hypoglycemia, all which contribute to hitting “the wall”
Carb loading the liver is easy. Loading the muscles, not so much. There are advantages and disadvantages to loading the muscles and each individual needs to decide whether they want to take the time to load. If they choose to load the muscles, they should practice well before the planned event and decide whether they’ll do a depletion loading or non-depletion loading. Load the right way- taper and intake the proper amount of carbs. Know there will be a bit of weight gain and potentially some bloating or discomfort. It’s just water. Practice it so you know how it feels versus taking it to a race.
There’s a ton more on this subject, maybe I’ll delve more into it later. For now I’m working on the other promised stuff…those incredible “mine is best” running diets.