Articles

Nutritional Strategy (Part 2).

Posted On: 01 February 2008
Category: Nutrition

 

 Written (03/10/2002 )

This has been a long time coming, but as promised, here’s a little piece on short-term nutritional strategies. By ‘short-term’ I refer to eating practices in preparation for particular events or during periods of extremely heavy or demanding training…

Carbo-loading

Boy oh boy, haven’t attitudes to carbo-loading changed? Since the 1960’s when it was discovered that the level of muscle glycogen in athletes was of particular importance during exercise, scientists set about finding ways of boosting this to ultra-high levels. Research has proven conclusively that higher muscle glycogen levels will extend time to exhaustion (meaning that you’ll last for longer) and allow an athlete to achieve more total work. This is because glycogen is held in limited supply within the liver and muscles and when it runs out, the body has to look for an alternative fuel supply.

Since we need a little bit of carbohydrate to get the energy out of fat, when the glycogen stores have been used up, the body then turns to a process called ‘gluconeogenesis’ whereby protein is converted to carbohydrate. This is a slow inefficient process and results in the breakdown of muscle tissue – not a good thing. When our stores of glycogen run dry everything starts flashing (those who’ve been there will know what I’m talking about) as blood glucose hits rock bottom and we lose power dramatically. This is called ‘bonking’ in cycling or ‘hitting the wall’ in marathon running.

The previous article Nutritional Strategies (part 1) discusses the importance of a consuming a diet rich in carbohydrate on an ongoing basis, but now we’re going to look at a few suggested techniques for super-loading the muscle glycogen stores for an enduro type event. It should be noted that carbo-loading might not be advantageous for events lasting less than 1½ hours as the loading process can leave the legs feeling a little heavy and tired. You do after all store 2.6grams of water with every gram of glycogen.

The Astrand regimen (1979) was the original carbo-loading plan and involved completing an exhaustive bout of exercise 7 days before the event. For the following 3 days he suggested eating almost exclusively fat and protein to deprive the muscles of carbohydrate, which increased glycogen synthetase activity (an enzyme responsible for glycogen synthesis). Then for the 3 days before the competition one should gorge oneself on all sorts of high carbohydrate foods. Exercise levels are also greatly reduced during this final week. This regimen has been shown to elevate muscle glycogen stores to twice the normal level, but has been criticised heavily as it subjects the athlete to great deal of unnecessary discomfort and the exhaustive bout of exercise 7 days prior to competition could leave the athlete under-recovered for the event.

The Sherman regimen (1981) provided equally high pre-competition muscle glycogen levels by simply introducing a training taper (reduced training volume) and following a mixed diet, then 3 days prior to competition, carbohydrate intake is significantly elevated. The low training volume and mixed diet prevented the low blood sugar levels, disorientation and discomfort associated with the glycogen depletion and fat/protein loading stages of the Astrand regimen.

The University of Western Australia regimen (2002) was recently outlined in a recent issue of Peak Performance magazine and I found this particularly interesting. The Australian research, which was published in Medicine and Science in Sports and Exercise, offers a very straightforward protocol. It involves performing a 3-minute maximal intense burst of exercise just 24 hours before the big event, the rationale being that high intensity exercise has been found to stimulate greater rates of muscle glycogen synthesis than moderate intensities. The aim during the 3-minute bout is to push lactic acid levels through the roof – the signal to initiate glycogen synthesis and although some may question this practice so close to an event, the researchers were confident that such a small amount of exercise wouldn’t compromise the effectiveness of the overall pre-event taper.

Within 20 minutes of completion of the 3-minute bout, the eating begins whilst enzyme activity is still vigorous. The aim over the next 24 hours is to consume 12grams of carbohydrate per kg lean bodyweight, which is a mighty large amount! Less than 10% of calories should come from fat and protein and 90% from carbohydrate – an impossible task without the use of a sports drink. In fact, the researchers revealed that about 80% of the carb calories came from a maltodextrin-rich drink called ‘Polycose’ - similar in basic composition to TORQ glucose polymer. It should also be noted that most of the high carb foods consumed should have a relatively high glycaemic index. The glycaemic index refers to the speed at which the glucose from the carbohydrate gets into the bloodstream (more on this in a later article).

Anyway, it turns out that not only is the University of Western Australia regimen the fastest glycogen-loading plan ever reported, but it also produced muscle glycogen levels which were significantly higher (198mmol per kg) than those achieved through traditional methods (131-153 mmol per kg).

Eating to recover during bouts of high-load training

This subject is covered in considerable detail in the following article on the Singletrackworld.com website:

Tired

The gist of this article is for regular and consistent intake of carbohydrate-rich foods while you’re training as well as at other times. According to Dr Melvin Williams (1998), author of ‘The Ergogenics Edge’ a diet with as much as 75% of total calories coming from carbohydrate is necessary for the 24 hours post exercise to ensure effective recovery. During very heavy spells of back-to-back training, I think it would be fair to assume that a diet of this order would be appropriate to optimise glycogen storage in the short-term. This would mean that protein and fat would represent only 25% of the remaining daily calories. Protein is a very important auxiliary fuel for endurance athletes and, according to research, should represent somewhere between 5 and 20% of daily calories, or you'll start metabolising your muscles. I have no doubt that most physiologists would agree to settle for around 15%. This doesn't leave much room for dietary fat, which although a substantial contributor to an endurance athlete's fuel supply, in it's dietary form as triglycerides it isn’t a useful nutrient. Your body will mobilize free fatty acids without protest from your subcutaneous stores (under the skin and around the organs). There's a practically inexhaustible supply of fat stored about the leanest of bodies!

You must look at your performance during spells of heavy training as being almost exclusively governed by your carbohydrate intake. This is a rather simplistic way of looking at the whole thing, but it will save you in the short-term. Ram the carbs down your neck before, during and after exercise and you’ll get through it. And for the long term, well that’s a different story and is not nearly so simple. Read the article below if you’d like to find out more about long-term recovery techniques:

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