For many years and even to the present day, the exercise science and textbooks classify exercise as being one of two types: aerobic or anaerobic. This classification refers to the metabolic energy systems required to perform either extended duration/low intensity exercise (aerobic) or short duration/high intensity exercise (anaerobic). Aerobic literally means “with oxygen” and anaerobic means “without oxygen”. This article provides some very basic information on anaerobic exercise and argues the very real possibility that this form of exercise according to the given definition, simply does not exist.
Different Energy Requirements – Different Energy Systems
During low intensity exercise such as walking, a large majority of the required energy comes from the use of fat as a fuel. Oxygen is required to convert fat into energy and is therefore called aerobic metabolism and the exercise it supports, aerobic exercise. This process of generating energy however is very slow and cannot generate energy quickly enough for higher intensity exercise such as running and sprinting. A different type of energy system is required for high intensity exercise – one that relies more heavily on the use of carbohydrate. This energy system is able to generate energy much quicker and does not require the need for oxygen. Thus exercise scientists have named this energy system the anaerobic energy system and the exercise it fuels, anaerobic exercise. It is important for the reader to note that energy systems work on an intensity continuum, that is at any given exercise intensity, a certain percentage of the energy yield will come from fat metabolism and a certain percent will come from carbohydrates. For anaerobic metabolism system to work at a high speed however requires the formation of a substance called lactate or lactic acid.
Muscle power output and oxygen demands
Recall from our article on High Intensity Interval Training (HIIT) [http://www.bossfitness.com/card-training.asp] we discussed the concept of intensity, power and power output. As exercise intensity and muscle power output increase, so proportionally does the oxygen demand of muscle. This oxygen demand is referred to as the volume of oxygen uptake or VO2. For the most part, as heart rate (an indicator of intensity) increases, so too in direct proportion does VO2. Traditional exercise physiology theorizes that as exercise intensity (running speed) progressively increases, the muscles become more and more anaerobic until a point occurs where oxygen uptake no longer increases, but reaches a maximum value and levels off. This leveling off has become known as maximal oxygen uptake or VO2 max. VO2 max is defined as the maximum amount of oxygen the body can use to produce work and is therefore a measure of the body’s maximum aerobic power. At the point where VO2max is noted, traditional exercise science proposes that the working muscles must be 100% anaerobic, leading to massive buildup of lactic acid which “acidifies” and shuts down the muscles, causing the individual to stop exercising.
Anaerobic exercise cannot exist since muscles never attain a truly anaerobic state
Professor Tim Noakes at the University of Cape Town prefers to call anaerobic activity “oxygen independent” activity since muscles never actually attain a truly anaerobic state. Noakes argues that if according to “traditional” exercise science theory the working muscles were to become anaerobic, then the heart, which is slave to the muscles for supplying oxygen (via blood flow), must become anaerobic first. Modern exercise science has failed to realize or consider that the heart, which is also a muscle, demands the same increased oxygen requirements with increasing exercise intensity as the working muscles do. Should the heart become anaerobic, then a heart attack would result and the exerciser would die. Clearly this does not happen on a regular basis in healthy exercising individuals. Noake’s documented research also points out that half of subjects tested in laboratory settings fail to demonstrate a leveling off of VO2 at exercise termination – in other words, their oxygen uptake was actually still going up when they stopped. Also, Noakes points to research that shows that lactate levels actually decrease as altitude increases. This so called “Lactate Paradox” is the exact opposite of what would be expected, since the traditional model of exercise physiology claims that as altitude increases and there is less “available oxygen”, there is therefore an increased potential for the development of anaerobic muscle. The previous explanations shoot holes in the concept of anaerobic exercise and also fail to explain what causes people to terminate exercise.
If lactate and anaerobic muscle do not limit maximal exercise then what does?
Prof. Noakes proposes that there exists a “central governor” somewhere in the body that informs the brain of the heart’s condition. Clearly, the heart must be protected from working so hard to supply the exercising muscle with oxygen as to jeopardize its own risk of becoming anaerobic and causing death to the body. Although it is unclear at this time the exact mechanism of its location or operation, Noakes proposes that the central governor somehow regulates the power output of the exercising muscles in order to protect the heart from overload. This regulation of power is suspected to occur via a decreased motor nerve activity to the working muscle via the motor cortex of the brain (part of the brain that regulates muscle activity). Recall that lactic acid generation is directly dependent on muscle power output – which would explain why muscle lactate decreases as altitude increases. A decrease in activation of the working muscle mass decreases the oxygen demand of the muscle, ensuring a sufficient blood flow (oxygen) to the heart.
It should be clear from this article that anaerobic exercise and anaerobic muscle in their defined form cannot exist during even extremely high intensity exercise. Some other regulating factor must be present in the human body to prevent it from “running itself to death.” While much research on the reasons for exercise termination needs to be done, for now it may be that “oxygen independent” exercise is a more accurate description of high intensity exercise instead of anaerobic exercise.
David Petersen is a Personal Trainer/Certified Strength and Conditioning Specialist and the owner and founder of B.O.S.S. Fitness Inc. based in Oldsmar, Florida. More articles and information can be found at [http://www.bossfitness.com].
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