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The Aerobic System

Posted by Filed Under: Science and Research

cardio.jpgIn the last article we discussed that ATP, regardless of the type of activity is the energy currency of the body. During aerobic activity, such as long distance running we require a constant energy supply over a long period of time. The aerobic system is able to supply this energy by using carbohydrates, fats and proteins from our body as fuel and converting them into simpler products that can be used in what is called the Kreb’s or Citric acid cycle.

The organelles known as mitochondria are the “powerhouses of the cells” and are the location where ATP production occurs by a process called oxidative phosphorylation.

When we train aerobically there are a number of physiological adaptations that occur that make our body more efficient at producing ATP:

  1. Increases in capability of mitochondria to make ATP by oxidative phosphorylation.
  2. Increases in number and size of mitochondria, and the enzymes associated with aerobic metabolism.
  3. Increased ability for muscles to mobilize fats for fuel, via increased blood flow in the muscle and more fat mobilizing and metabolizing enzymes.
  4. Increased carbohydrate oxidation and less lactic acid build up.
  5. Selective hypertrophy of the slow twitch muscle fibers, which have more mitochondria and more aerobic metabolism enzymes versus fast twitch fibers.

So how does this apply to running a marathon?

Running performance in endurance events depends to a large extent on the nutritional support for the muscles, that is, how much fuel and hence energy can be supplied to them. More specifically, endurance event performance depends greatly on how much glycogen has been stored in the muscle (and liver) prior to exercise.

Glycogen is broken down into glucose and it is glucose that is preferentially used for energy in aerobic activity. Fats and to a much lesser extent proteins are also used for energy too. Utilization of fat for energy is stimulated by the hormones norepinephrine and epinephrine which are released during exercise. This causes another substance called hormone sensitive lipase to break down fats so that they can be converted to glucose and used for energy. In fact, the longer the duration of the event, the more fats are utilized for energy, and may approach 50-80% of the energy supply as the glycogen supply is depleted.

Of note is that energy drinks with a glucose solution of 2-2.5% can help spare glycogen and provide up to 30 to 40% of the energy required during endurance events such as a marathon.

So How Can The System Work For You?

Try coffee before a race. Caffeine has been shown to “jump start” the fat burning process so that glycogen can be spared.
Stock up on glycogen stores by having a complex carbohydrate rich meal 3 hours prior to racing, and a sports drink 30 minutes before racing.
Reload with carbohydrates and proteins within 1 hour to 90 minutes after training. Growth hormone released post workout helps to selectively replenish these a few percent more effectively than if you replenish later on.
If you are going to take in carbohydrates during your long distance race, start doing it earlier rather than later. Studies suggest that with activity, there is poorer absorption from the stomach the longer the activity goes on. This is due to a shunting of blood to the active muscles versus the gastrointestinal system.

Whenever you try a new loading or hydrating regimen, try to use common sense and the basic understanding of how the body works to guide you in your strategy. If you are going to try something new, never ever try it for the first time in a race! Use your training runs as the testing ground for anything new. If it works in training, then you can try it during competition.

To all of our readers, much of this article is a simplification of detailed physiology and biochemistry to better understand the general concept of how these systems work. If anyone wants a more detailed explanation of these processes a good reference book is the Textbook of Medical Physiology, by A.C. Guyton MD, published by W.B. Saunders Company.

About Lee Miller D.C.

9536 - 87 Street Edmonton, Alberta T6C 3J1 Phone: (780) 426-6777 Fax: (780) 469-6930



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