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Our body's ability to work aerobically at a very high level may be limited by the supply of oxygen through our lungs or the ability of the muscles to utilize the oxygen supplied to it.

A high maximum level of oxygen uptake (VO_2max) is a vital component of successful endurance performance. The factors limiting VO_2max are of considerable interest to exercise physiologists, and have for a long time been a topic of discussion in the literature.

The transport of O₂ from the lungs to the tissues involves many steps including the diffusion of O₂ from air to blood in the alveoli, its transport via the arterial vasculature, to the uptake of O₂ by the body's cells. Many of the steps in these processes have been postulated as being rate limiting.

Two separate schools of thought have emerged on the factors limiting O₂ transport, and therefore VO_2max, based on the limitation being 'central' or 'peripheral’ (Sutton, 1992). The central mechanisms encompass the steps involved in the O₂ delivery from the air to the muscles, consisting of the pulmonary and arterial systems. Peripheral mechanisms involve the extraction and utilization of O₂ by the exercising muscles.

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There a evidence which supports each of these areas of limitation, though it may not be simply a single step that limits the total system. The site of limitation may vary depending on the level of specific factors. A change in one parameter can cause another to become limited. For example, if blood flow to the muscles is inadequate, then the diffusion gradient may become less and therefore become the limiting factor (Sutton, 1992). Wagner (1992) believes all the steps in the O₂ pathway interact to determine VO_2max, and increasing and decreasing the transport capacity of any one step leads to an increase or decrease in VO_2max respectively.

The complexity of the processes involved, and the equivocal results of the many studies in this area, would indicate that the site of limitation varies between individuals, and possibly at any one time depend on the state of associated parameters.

References

• Sutton JR. Limitations to maximal oxygen uptake. Sports Med. 1992 Feb;13(2):127-33.
• Wagner PD. Gas exchange and peripheral diffusion limitation. Med Sci Sports Exerc. 1992 Jan;24(1):54-8. 

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Related Pages

• Lung function tests
• The anatomy of the lungs
• Exercise Physiology

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The above information is presented as a general guide. The author and publisher take no responsibility for any possible consequences of any treatment, procedure, exercise, action or application of medication based on this information. See more: Disclaimer.