Individual Considerations for Glycogen Reduction as a Fight Week Strategy
“Take an 80kg athlete for example. By using the following assumptions it would be suggested that they would be able to lose 441grams and 1850-3700grams from liver and muscle glycogen with the associated bound water. That’s a difference of 1.85 kilograms and when it comes to making weight, that’s a lot.”
Something we do a lot as Dietitian’s that annoys a lot of people is overuse the term ‘it really depends on the individual’. I understand how frustrating it is, as most people want a generic one size fits all answer, but the fact of the matter is that it’s completely true. A great example of that is glycogen depletion, or more accurately glycogen reduction.
Although we know it is an effective strategy to lose weight during fight weeks, what we don’t really know is how much glycogen we have to lose during that week. It’s really individual.
What we do know is that if you reduce dietary intake of carbohydrates and complete high intensity exercise, the amount of glycogen in various tissues, mainly the muscles and liver, will be burned to support that exercise and other bodily functions. This breakdown of stored glycogen as well as the removal of the water that is attached to it (2.7grams of water for every 1gram of glycogen) causes the person completing this to lose weight.
We use this technique all the time with combat athletes. It’s generally accepted that this method will cause a total body mass decrease of 2-4% body weight. But there are a few assumptions we make to get that number.
To calculate the amount of glycogen someone has in their body we make the assumption that the amount of glycogen in the muscle and liver equals 1-2% and 8%, respectively, of the dry weight of those tissues. To make that assumption we need to know the size of the liver, and how much skeletal muscle mass the individual has.
The assumption that is generally made is that the average liver weighs 1.5kg and the average athletic male body is comprised of 60-65% muscle mass. The liver is bound by the design outlined in the human genetic code, so the variance in its size will be more proportional to the human it is inside. However, body composition can vary greatly depending on genetics, training status, and the type of training completed. Even once you have a body composition, determining muscle mass can be tricky.
Body composition scanners such as DEXAs express total lean mass in grams where skeletal muscle mass needs to be assumed as a percentage of that number. Again, this will depend on many factors of the individual. To add to this, the type of muscle fibre, whether is a aerobic, anaerobic or a hybrid, will also play a role in how much glycogen is held within the muscle mass.
What’s the point of going over all of that? To highlight how much ‘assuming’ is made in getting that number. As the old saying goes ‘the more you assume, the greater your degree of uncertainty gets’.
Despite all of these assumptions, we know this strategy works. We do it all the time with athletes, but to bring this back to why treating this on an individual case is important, we can look at the variance that exists from these numbers.
Take an 80kg athlete for example. By using the following assumptions it would be suggested that they would be able to lose 441grams and between 1850-3700grams from liver and muscle glycogen with the associated bound water. That’s a difference of 1.85 kilograms, and when it comes to making weight, that’s a lot.
For anyone that has completed fight weeks with athletes you know that 1.85kg less or extra in the bath or sauna can be the difference between a bearable time and a not so bearable time.
So how do we reconcile this for effective practice? You treat it by a case by case basis. Where possible, run trial fight weeks or at least experiment with the different fight week strategies to assess how much the individual actually loses. You assuming they will lose 4kg and then losing 2kg will make a difference come fight week.
Remember the aim of the game is to complete this process in the most least harmful and controlled manner possible. To be able to do that you need to be informed about your athlete. Use the studies as a guide, but use your ability as a Practitioner to make that information applicable to the individual in front of you.
Jordan Sullivan – Head Dietitian TFD
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