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GlycoSource Q&A

Want a deep-dive on the science behind Science Fitness' flagship GlycoSource?

We held a Q&A session with Professor Roderick King, the head of the development team for GlycoSource and Carnegie Professor of Sport & Exercise Biochemistry a Leeds Beckett University. We asked him to explain the mechanics behind glycogen, the very fuel GlycoSource is based around.

Hi Professor King. Straight in - what is Glycogen?

Glycogen is a polymer of glucose in which all the glucose molecules are linked together in a shape that resembles a tree. The molecule is found mainly in muscle and liver but small amounts are found in kidney and brain. Glycogen is a storage carbohydrate and is used whenever energy demands are critical. Quite simply the cells and tissues that need to produce energy break the glycogen down at a controlled rate to produce glucose molecules that are used in energy metabolism.

And how can that affect exercise?

Consider exercise such as running and cycling where the muscles in the leg are the main powerhouse for motion. These muscles use some fat but also large amounts of glucose produced from breakdown of glycogen within the muscle fibres. This glucose is metabolised within the muscle fibres to produce vast amounts of ATP that powers the contracting muscle.

This process must happen no matter the extent of the exercise, be it sprints at a very high effort or a more subdued but sustained effort. Sprinting tends to be a short period of very high energy demand lasting usually for less than a minute whereas sustained effort can only work at a lower energy production rate but can go on for hours such as in a marathon or long distance cycle race.

Does Glycogen deplete during and after exercise?

Glycogen is a wonderful fuel for energy production in muscle but there is a limit. This is because the reserves of glycogen in muscle are not infinite, the quantity is limited and once it’s almost used up it is no longer possible to produce energy at the same rate. The problem for muscle could be dire, but there is some relief from glycogen stored in the liver. This can be broken down to glucose and passed in the bloodstream to the working muscles where this glucose enters the muscle and helps to supply that from the muscles limited glycogen.

Obviously when you exercise hard for a long time the reserves in both muscle and liver get used up and this then limits performance. Basically fatigue sets in and you may come to a halt. There is no other solution other than to rest and recover and re-build those glycogen reserves.

Can Glycogen be replenished?

Glycogen reserves are built back up whenever the body has sufficient nutrients and is typically accomplished in rest periods. This process occurs naturally during the usual events and lifestyle of a typical day. It is inevitable that providing sufficient nutrients go in, both liver and muscle glycogen is re-built. For the average person glycogen reserves vary up and down throughout the day and reflect periods of activity when they are used up and periods of replenishment after meals when they are re-built. First thing in the morning liver glycogen is low and if you have had an early morning run then muscle glycogen will also be low. It follows that breakfast with carbohydrate is essential to rebuild those lost reserves.

For the person who enjoys exercise, however, and those that train and compete regularly, it becomes more critical.  After exercise and especially if you want to maintain a competitive edge, it is a good idea to eat carbohydrates soon after exercise. Failure to rebuild the reserves of glycogen in muscle and liver in an optimum way results in below par performance and a low ability to train and compete effectively. It is no surprise that the available scientific evidence indicates that those with the greater reserves of glycogen are able to perform well and are less susceptible to fatigue whilst those with the lower reserves are very limited in their performance capacity.

What role do different carbohydrates play in the replenishment of Glycogen?

Carbohydrates that we ingest ultimately may form the glycogen in muscle and liver. The process starts as we eat. Food enters the stomach after swallowing where the acid environment helps enzymic degradation of protein. It is only when the contents are forced into the duodenum and small intestine that serious digestion of carbohydrates begins where pancreatic enzymes in an alkaline environment break down the complex carbohydrates we may have eaten.

Any simple carbohydrates that we take in, like glucose, are already in a state for absorption but it is essential that complete digestion of all the complex starches, maltodextrins and other large carbohydrate molecules has been completed before full absorption into the bloodstream can occur. Thus the body may acquire glucose, fructose and galactose depending on the original food eaten.

These simple sugar molecules pass in the bloodstream round the body to all cells, tissues and organs. What is important for us is their use to form glycogen. This is where metabolism has intrigue and evolved functionality.

And what are these sugar molecules?

Each one behaves quite differently depending on their uptake. Glucose can be taken up by muscle and be used to form new glycogen whereas in the liver glucose can be taken up but can form glycogen by two routes, a direct one and an indirect one.  Although fructose can be taken up by muscle at a low rate it can also be taken up by liver and in both cases be used for formation of glycogen. However, galactose is not taken up by muscle but is very effectively taken up by liver and used in a specific metabolic pathway to make glycogen and glucose.

What do you feel is the most important aspect in the role of glycogen in endurance sports?

The question for sports performance becomes one that addresses the speed, efficiency and effectiveness of glycogen re-synthesis purely to rebuild capacity and ensure subsequent performance. Competitive edge is essential; the ability to train continuously and compete to win is definitely worth striving for. It follows that scientific research focussing on this area to provide a sound evidence base for practise. The problem hinges around the nutritional mix, its prescription and efficacy.

What is now known is that glycogen re-synthesis is a very important part of recovery, that to be effective the constituents supplied must be critically balanced and of specific types, the timing and dose must be carefully organised and controlled. Get this wrong with too little dose at the wrong time and glycogen synthesis is compromised to the detriment of performance. Get this right with good prescription and formulation and the resulting optimisation gives enhanced performance!

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