Fueling for Performance

Hanny offers her advice for eating on the run
Hanny offers her advice for eating on the run

After the shenanigans of the recent Coast2Kosci race here in Australia, it’s back down to business with some more advice to help you runners make the right decisions. With Christmas nearly upon us, many of us will be thinking about food, and this article is exactly that. Fuel is such a critical part of succeeding in an ultra that when we get it wrong, or race can go downhill very very fast.

We welcome back the ever knowledgeable and highly qualified, Hanny Allston from Find Your Feet back to pages to give us the low-down on how to fuel properly for your races…

Humans: Superior to eating on the run

The human body is amazingly adaptive.  Whilst we might not be the fastest or most powerful species on the planet, we can outrun any other animal before fatigue stops us. Even under extreme distress, we can continue to place one foot in front of the other for a very long time.  This is why the human race has been able to survive and thrive, even under extreme circumstances such as droughts & famines.

What allows us to run over long, long periods of time is our ability to utilize fat stores for physical energy & replenish our energy stores as we exercise to maintain the function of our driving force – the central nervous system.  For example, a cheetah cannot gulp down some food as he runs after his prey.  A camel doesn’t ingest fluids or food as he plods along.  A horse cannot chew grass as he gallops across a field.  But we can and it is this ability what gives us the capability not to ‘Bonk’.

Bonk– whilst the term has some inappropriate definitions that are certainly not related to this article, it is also a well-known term associated with endurance sports.  Otherwise known as hitting the wall, the ‘bonk’ describes a condition caused by the depletion of the body’s glycogen energy stores located in our muscles, liver and blood stream.  The strange thing about bonking is that some runners reach this point earlier than others.  Further to this, some runners can run at much faster paces than others before the wheels begin to fall off.   This raises the questions:

  • What are the factors that contribute to the rate of glycogen depletion?
  • How can this help you to choose a fueling strategy to suit your race?

Glycogen Depletion

Recent studies have identified three key factors that affect the rate of glycogen depletion:

  1. Aerobic capacity (or VO2 max) is the maximum amount of oxygen that the body can utilize during an exercise session.  It is possible to improve aerobic capacity over time through training.  Even small amounts of physical activity can positively affect your capacity and improve the efficiency in which you utilize glycogen stores.  Conversely, increasing age, illness, and decreased training can negatively influence your aerobic capacity.
  2. Increasing lean muscle mass will have a positive impact in many ways on your running performance.  Aside from strength gains, increasing your lean muscle mass will allow you to hold a greater volume of glycogen for utilization during exercise.

    Ughhhh... we've all been there!
    Ughhhh… we’ve all been there!
  3. Increasing your glycogen concentration will provide a greater reserve when exercising.  Glycogen concentration is the amount of stored glycogen per storage volume in the liver & muscles.  Glycogen concentration will be particularly influenced by diet & training loads.  A diet low in energy & carbohydrate combined with higher training volumes will prevent glycogen storage.  Conversely, tapering training and increasing carbohydrate intake will positively influence glycogen concentrations in the muscles.

Another determinant to how effectively we preserve our glycogen stores is how efficiently the body utilizes other energy sources. As distance athletes, the most important source of energy we have is fat.  Fat combustion provides the largest release of energy over any of our others fuel sources and the body will prioritize this energy source to preserve our glycogen stores for higher intensity effort & maintaining the function of the central nervous system.  However, whilst fat provides an excellent energy source for distance runners, the body cannot solely rely on it.  Ketone bodies, the waste products of fat combustion, are toxic to the central nervous system & brain.  Accumulation of ketone bodies and glycogen depletion will result is in lethargy, decreased performance and clarity of thinking, known as central fatigue.

Preventing Bonking

There are two important considerations for preventing bonking.

  • Training the body’s energy systems in training is fundamental to utilizing fuel stores at the appropriate times. For example, long slow distance running and tempo runs will help to ensure that the body quickly converts to using fat stores to preserve our glycogen supplies.  Conversely, speed & interval training will utilize glycogen for fuel. Training the body to utilize these stores also serves to teach the body how to cope with the adverse side effects of each fuel source.
  • Replenishing glycogen stores throughout a race is critical to maintaining the function of the brain & central nervous system, and to provide a source of energy for periods of higher intensity.

Fueling strategies for optimal performance

The sports nutrition market is vast and every brand claims to give you the edge.  Each has a different philosophy for refueling on the run.  How do you choose and who do you listen to?  The most important thing to understand is that we are aiming to maintain our glycogen stores without upsetting our bodies.  During exercise the gut system shuts down to shunt blood away to the working muscles.  The body becomes very selective about the absorption of food and stomach distress is a very real issue for many runners.  Therefore, we need to keep our fueling strategy simple and appropriate.

What food will you be eating in your race?
What food will you be eating in your race?

Glycogen is a multi-branched polysaccharide of glucose and is stored in the muscles and liver.  Muscle glycogen is converted into glucose by muscle cells and liver glycogen converts to glucose for use throughout the body including the central nervous system.  Therefore, the optimal energy source for an athlete is glucose.

Glucose provides the most instance energy source for the brain and central nervous system because it is the most easily absorbed from the gut system into the working cells.  It is found in many carbohydrate foods but for athletes, the richest source of glucose is in sports gels.  These are designed to hold the highest energy concentration per quantity of substance and in a consistency most absorbed by the stressed gut.  However, not all gels are prepared equally.  Avoid gels high in sucrose and concentrated fructose, and watch for those pumped with additives such as magnesium, potassium & flavorings.

Glucose is not Sugar!

There are many different forms of sugar found in sports products.  Aside from glucose, two notable ones commonly used are sucrose and concentrated fructose.

  • Sucrose, otherwise known as table sugar, is pumped into most confectionary or sweet drinks marketing themselves as sports drinks.  Sucrose is so highly processed that when the gut processes slow during exercise, it is poorly absorbed, remains in the intestines and begins to ferment.  It is renowned for causing stomach upsets and not actually generating a ‘kick’ during exercise.
  • Fructose is a natural sugar found predominantly in fruits.  It is broken down into glucose in the liver and due to this, have a lower Glycemic Index than glucose.  The problem with fructose is when it is refined… and concentrated fructose is everywhere in the sports nutrition market!  In its refined form, fructose is incredibly sweet and hence tastes like energy. It was first added to sports products to provide a more lasting energy source during exercise.  The problem with concentrated fructose is that during exercise the liver processes slow down, resulting in poor absorption from the gut and less energy released for utilization by working muscles.  Like sucrose, fructose can cause significant stomach upsets and should be consumed in moderation.

Choosing your fueling strategy

Selectively taking on board small amounts of fuel frequently is superior to large volumes infrequently.  For this same reason, energy dense foods will be better tolerated than fluid-forms of energy (i.e. liquid energies such as sports nutrition made up from powders).

It is recommended that athletes ingest glucose rich energy every 30-40 minutes, depending on how hard they are working and how efficient they are as a runner.  A smaller, more efficient athlete will cope with longer between refueling whilst a large, less efficient runner will need to replenish their energy more frequently.  It is recommended that athletes set a watch alarm to remind themselves to refuel and avoid glycogen depletion.  Once glycogen depletion occurs during a race, it is very hard to replenish your stocks enough to maintain performance.  It will only be after exercise has ceased that this can occur.

As mentioned, the richest sources of glucose come from energy gels.  Some people, such as myself, struggle to consume just gels and I like to alternate between gels and other glucose-rich energy sources every 40 minutes.  Other great sources of glucose come from sports bars, muesli bars, pure-glucose jellybeans, glucose tablets or even honey.

Glucose energy is the most optimal fuel source for athletes during higher intensity distance events.  It is the least demanding on the gut system and the most readily absorb by the working muscles.  Further to this, it is the only source of energy that can be utilized by the central nervous system, thus maintaining optimal brain function throughout the race.  Refueling with glucose every 30-40 minutes will help to avoid glycogen depletion and stave off hitting that wall.  Applying appropriate training and practicing refueling during longer runs will ensure optimal performance on race day.

Dan on Twitter
I'm a mediocre runner who can bat above his average when I train hard. A man of extremes, I do enjoy everything life offers and consider it an absolute pleasure just to be able to put one foot in front of the other and let my mind wander somewhere different.

3 thoughts on “Fueling for Performance

  1. Great read and sound advice. Would be fascinating to read about depletion training and how to do it…It’s a tightrope between overly fatiguing yourself then subsequently losing a week to recovery and conditioning your body to do it.

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