Aerobic Capacity

by Patti and Warren Finke, Team Oregon
The physiologic basis of performance in aerobic sports such as distance running is aerobic work capacity. This trait is largely inherited and varies by as much as 300% between individuals, explaining the wide range of performances observed in any given road race.

VO2 Max

Exercise physiologists measure a quantity known as VO2 Max, your capacity for Oxygen uptake, aerobic energy transfer, or your aerobic "horsepower". An improvement in VO2 Max increases the amount of work you can do or means that you can run faster and/or farther. The variables that influence VO2 max are heredity, state of training, age, sex and body composition (the amount of lean tissue). Heredity is the most important determiner of VO2 Max. The best way to be faster is to pick faster parents. Even though heredity determines where you start, training can increase performance by 20% to 25% with some changes of up to 50% reported. Having an idea of your starting point is important in setting ultimate performance goals. Following an elite athlete's training schedule will not make you as fast as that athlete if you lack the inherent potential.

VO2 Max is usually measured in terms of milliliters of Oxygen consumed per kilogram of body weight per minute. The highest VO2 Max's are found in cross country skiers, distance runners, cyclists and swimmers. Males in general have higher VO2 Max's showing the contribution of sex and body composition. Some selected examples for Olympic-caliber males are: cross country skiers, 85 ml/kgmin; middle distance runners, 80 ml/kgmin and cyclists 75 ml/kgmin. The average sedentary male is at 45 ml/kgmin while the average sedentary female is at 39 ml/kg min. Olympic caliber female examples are: cross country skiers, 65 ml/kgmin; runners, 58 ml/kgmin and swimmers 55 ml/kg min. Some elite runners that you might know are Alberto Salazar reported to be 80 to 82 ml/kg min, Steve Prefontaine at about 85 ml/kgmin and Joan Benoit Samuelson around 78 ml/kgmin.

How can you find out what your potential is or how do they test for VO2 Max? Treadmill tests in an exercise physiology lab are fairly complex and expensive, but can accurately measure VO2 Max. Submaximal or maximal treadmill tests done in the doctors office or fitness facility use heart rate to predict VO2 Max within 10% to 20% of the actual value. Timed runs of various distances such as Ken Cooper's 12 minute test can be quite accurate for runners. Other fitness tests such as step testing or bicycle ergometery are not as accurate for runners because of the specificity of exercise. We use a computer program we have developed which uses race performance at any distance and has correlated quite well with physiologic VO2 Max tests. This computer program is part of the "splits" program which has been used by Nike for the Cascade Run Off, Portland Marathon and other major races including the Boston and New York Marathons. The program gives predictions of race performances as different distances and ranks you with other runners of your age and sex. We use this program to determine goals and training paces for runners in our clinics and runners we coach.

How Do You Stack Up?

By itself, VO2 Max is not a useful measure of your performance. What you really want to know is how you compare with others. Seeing how you rank with other runners in the US can be done using the following graphs. The data was collected by the TAC National Running Data Center from all over America in 1986. It is probably still pretty representative. If you plot your best 10K time vs your age, you can see how you compare.

In Oregon we have a high percentage of runners within the top 1%, especially in the womens and masters categories. Elite national and international class runners are in the top 0.1%.

Body Composition The contribution of body composition to VO2 Max is evident as we look at the units used in the measurement of oxygen consumption (amount used over weight and time, mg/kgmin). Men, in general, have more muscle and less fat than women and can usually run faster. This does not mean however that some women cannot run faster than some men and, in fact, elite women athletes run faster than average male runners and about as fast as top mens masters runners. Body type and muscle type are inherited. About 60 - 80% of how fat or lean you are is also inherited. You cannot change body type, some muscle fiber is convertible and body fat, for most of us, can be changed. Elite runners both male and female tend to have long slender endurance muscles, small bones and low body fat.

How can you determine your body composition? The way considered most accurate is underwater weighing based on body density and is done at PSU and several local hospitals. It is important for runners that residual volume (the amount of air left in the lungs while underwater) is either measured or estimated by height weight tables. Some research has shown that spirometry, a technique often used, may not give a good estimate for runners because their lungs can retain more air in the tissue. The next best and most convenient body composition testing is caliper measurement of skin folds. This is based on the fact that about 50% of fat, both essential and storage, is under the skin. The tricky part here is that the person doing the measuring must be well trained and experienced with athletes. Skin folds are measured at local hospitals and health clubs. Ultrasound measures the underskin fat thickness like calipers and can be accurate, but is based on a measurement of one area. Electrical impedance is a favorite at athletic clubs because it is easy to do and is "hi tech". The literature reports and practical experience have shown that it may be accurate for average people, but can be unreliable in runners. Impedance is based on body water and electrolyte balance and testing needs to controlled for time from last exercise session, eating, monthly cycle for females and room temperature. The key to useful application of body fat testing is to remember that it is an estimate and is more useful in measuring relative changes rather than absolute amount.

What should body fat be? Every runner we know is always saying "I'd be so much faster if I lost 10 pounds", this is usually said while stuffing in some kind of food. We all have some essential fat including brain tissue that we need to be healthy The amount for males is about 3%. Because of wider variations in body type the minimum varies in women with 12% being a reasonable number. Being too lean can be harmful resulting in chronic injury and illness problems; it may be dangerous in women when a cessation of the menses causes calcium depletion in the bones leading to stress fracture and osteoporosis. The healthy range for men is 5 -25 % and 14 -30% for women. The athletic norms are 5 - 10% for men and 14 - 18% for women with fitness norms being up to 15 % for men and up to 22% for women. The norms we're giving come from the norms of Jackson Pollock and from lots of practical experience. We have found that when there is a balance between food taken in and exercise done, the body picks a body fat range that is healthy for it. Some of us, no matter how much running we do, will never be as thin as those fine boned elite runners. The key is to eat enough to fuel your exercise, have enough fat to be injury and illness free, and enough lean tissue to help you to run fast.

Aging

Is it not strange that desire should so many years outlive performance?
- William Shakespeare

Runner's times get faster up to 5 - 9 years after they start running, regardless of their age! The VO2 Max may actually peak within 6 months to 2 years, so how can you still improve performance? One reason is that you are able to run at a higher percentage of VO2 Max for a longer time because of increases in anaerobic threshold. The anaerobic threshold is the point when increasing intensity of exercise results in an accumulation of lactic acid impairing performance. Improving anaerobic threshold means that you can run harder for a longer period of time without going into anaerobic metabolism and accumulating the dreaded and painful lactic acid. Both Alberto Salazar and Joan Benoit Samuelson were noted for being able to run marathons at a high percentage of their VO2 Max's.

Another reason for improved performance over time is a change in running efficiency or economy. The more you run the better you develop motor skills related to running. Training for specific pace ecomomy is an important part of preparation for racing. We will deal with this topic fully in another article.

Does age eventually catch up with you? Yes, we all know younger runners are faster; that's why we have age group racing. VO2 Max tends to increase until about age 25 when it starts to decline (see 10km data in the figures above). The knowledge of the rate of decline has changed in recent years with studies of the same runners over 20 years spans. Previous estimates were studied using people in various age groups, not the same people as they aged. the rate of decline was thought to be 1% per year, but recent studies have shown that continuous training can slow that down to a much smaller percentage. We have seen spectacular performances for masters runners in the last few years as runners have kept racing through their 40's and 50's. Being over 40 is not a reason to take up a different less strenuous sport, but may mean you need to train smarter. Recovery time increases with age hampering the ability to train at the same levels as when you were younger. This may account for much of the loss in performance.


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