When embarking on a new exercise program, there are many factors to keep in mind. One must decide on the frequency of workouts, their duration, and most importantly, their intensity. For more seasoned athletes, these factors are often broken down into much more specific areas; one such area is the consideration of VO2 max.
VO2max has commonly been defined as the highest rate of oxygen consumption attainable during maximal or exhaustive exercise. Put more simply, this is point during a workout at which oxygen consumption reaches a plateau. It can also be viewed as an indicator of an individual’s maximal aerobic capacity. VO2 max is usually measured in milliliters of oxygen utilized per kilogram of body weight per minute. This enables the number to be expressed as a value relative to body weight, since oxygen consumption as well as energy needs differ based on the size of the individual. In some literature, VO2 max is also expressed relative to the body’s surface area. This becomes a useful tool when comparing children to adults, or contrasting oxygen uptake between the sexes.
Why is the concept of VO2 max important to athletes? It is considered an excellent determinant of an individual’s cardiorespiratory endurance as well as his aerobic fitness or potential. This knowledge can be particularly useful to the athlete who is training for an event at a higher altitude, such as mountain-climbing or marathon-running. Before embarking on a discussion of how oxygen consumption is affected by altitude, however, it is important to have a basic understanding of the physiological factors within the body that work in concert to determine the VO2 max. To this end, two theories have been proposed to help explain these various processes:
1. Utilization Theory: Proponents of this theory hold that one’s aerobic capacity is limited by a lack of sufficient oxidative enzymes within the cell’s mitochondria, often referred to as the powerhouse of the cell. It is the body’s ability to utilize the circulating oxygen supply that determines aerobic capacity. Some studies have shown that oxidative enzymes as well as the number and size of the cell’s mitochondria can actually increase with functional training. This leads to improved oxygen utilization, and hence to an improved VO2 max.
2. Presentation Theory: Proponents of this theory suggest that aerobic capacity is limited by the ability of one’s cardiovascular system to deliver available oxygen to active tissues. Studies have shown that an increase in blood volume, maximal cardiac output, and improved perfusion of blood into the surrounding muscles account for any changes observed in VO2 max associated with functional training.
While both of these theories present strong evidence, it has been concluded that it is indeed the supply of oxygen that becomes the major limiting factor when it comes to endurance performance.
Another term often seen in conjunction with references to VO2 max is stroke volume. Stroke volume is a measurement of how much blood the heart pumps out of the ventricle with each beat. In athletes, stroke volume increases with functional training. This reduces the number of times the heart needs to beat per minute, because it is pumping out more blood with each beat. Cardiac output, therefore, is the product of heart rate and stroke volume. Based on the information presented here, you may be getting an idea of how altitude may affect an individual’s maximal aerobic capacity. VO2 max decreases as altitude increases above 1600 meters. This closely approximates the altitude of Denver, Colorado. For every 1000 meters above this level, maximal oxygen uptake decreases even further, by approximately 8-11%. This decrease is mainly due to a downward slide in maximal cardiac output. Since we just learned that cardiac output is dependent upon stroke volume, this would make sense given the fact that stroke volume is decreased at high altitudes due to the immediate lowering of blood plasma volume. In fact, plasma volume can decrease by as much as 25% within the first few hours of exposure to altitude, and requires a few weeks to plateau.
A decrease in one’s maximal heart rate is also observed at higher altitudes, such that the overall effect is less oxygen being released from the blood into the muscles. A smaller number of available oxygen molecules per given amount of air means that increased breathing is required to consume the same amount of oxygen to which the body has become accustomed at sea level.
With all of these altitude-related changes occurring while the body is at rest, it is easy to see how exhaustive exercises such as climbing or running could seriously impact an athlete’s performance. Studies done by the U.S. Army Research Institute of Environmental Medicine have shed an interesting light on this topic. While it seems that strength and the ability to perform short, intense activities are not especially affected by altitude, long-term aerobic work is significantly hampered at higher altitudes. Tasks require more time to complete, and more rest breaks are needed in order to work efficiently. Thus, intense functional training engaged in at higher altitudes must allow for these differences.
Whether exercising at altitude or at sea level, an understanding of VO2 max can enable an athlete to fine-tune his aerobic potential. While not a great predictor of success in endurance events, VO2 max can certainly be utilized as a training tool. It’s just one more parameter in a long list of cardio-respiratory functions that can help an athlete gain that highly coveted competitive edge!
Cathleen Kronemer is an AFAA-Certified Group Exercise Instructor, NSCA-Certified Personal Trainer, competitive bodybuilder and freelance writer. She is employed at the Jewish Community Center in St. Louis, MO. Cathleen has been involved in the fitness industry for 22 years. Look for her on www.WorldPhysique.com, and feel free to contact her at [email protected]. She welcomes your feedback and your comments!
References
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-Wilmore JH and Costill DL. (2005) Physiology of Sport and Exercise: 3rd Edition. Champaign, IL: Human Kinetics
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-Wilmore JH and Costill DL. (2005) Physiology of Sport and Exercise: 3rd Edition. Champaign, IL: Human Kinetics
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-Costill DL, Thomas R, Robergs RA, Pascoe D, Lambert C, Barr S, Fink WJ. Adaptations to swimming training: influence of training volume. Med Sci Sports Exerc. 1991 Mar;23(3):371
About the Author
Cathleen Kronemer is an AFAA-Certified Group Exercise Instructor, NSCA-Certified Personal Trainer, competitive bodybuilder and freelance writer. She is employed at the Jewish Community Center in St. Louis, MO. Cathleen has been involved in the fitness industry for 22 years. Look for her on www.WorldPhysique.com.
She welcomes your feedback and your comments!
