Treadmill tests estimate fitness level

By DAN STRAYTON
As published May 2, 2007

I recently completed a fitness test on the treadmill at my health club but I’m not sure what the results mean. It gave me a number of 40 and said I was “average”. What does this mean and what could affect my results? – Ron, Mt. Airy

Dear Ron,

The fitness tests on exercise equipment are intended to estimate your cardiovascular fitness, also termed your aerobic capacity. The key word there is estimate – these tests are not directly measuring your cardiovascular fitness level and will have some degree of error inherent in them.

Your aerobic capacity is a measurement of your body’s ability to take in and utilize oxygen during exertion. Aerobic capacity is also known as your maximal oxygen uptake, or VO2max. The number you saw displayed by your treadmill was your VO2max expressed in terms of the amount of oxygen your body can consume relative to your bodyweight.

So, in your case, you had a VO2max of 40 ml/kg/min, meaning, at maximal exercise, you can consume 40 milliliters (ml) of oxygen per kilogram of body weight (kg) per minute (min). Very technical, I know.

A highly fit individual, particularly one who performs a great deal of aerobic exercise, will have a higher VO2max than the average person. The highest measurements usually occur in elite long distance runners and cross country skiers, sometimes reaching as high as 80 ml/kg/min – that’s an enormous aerobic capacity!

“Average” depends on age and gender, with the average woman having a lower capacity than the average man and an older person having a lower capacity than a younger one. You can improve your aerobic capacity by performing cardiovascular exercise on a consistent basis at a level that challenges your cardiovascular system.

A higher aerobic capacity means less work for your heart. When you begin to exercise, or perform any physical exertion, your muscles start demanding more and more oxygen. As blood pumps past your muscles, they try to extract as much oxygen from the blood stream as possible.

If your muscles need more oxygen than they are getting from the current blood flow, your heart will need to speed up to deliver more blood, and oxygen, to the area. Thus, as your exercise intensity increases, your heart rate increases to meet the demand of the working muscles.

An aerobically trained individual can carry more oxygen in his/her blood stream and has muscles that are better able to extract this oxygen as the blood passes. This means that, since the muscles are getting more oxygen from the same amount of blood, the heart will not need to speed up as quickly and will not need to work as hard to accomplish the same amount of exercise.

That is why one person can walk on the treadmill at 4.0 mph and have a heart rate of 115 and another person may have a heart rate of 135 or more. The first person is more efficient at taking in and using oxygen and can accomplish more work at a given heart rate.

The test you refer to on your treadmill is, again, only estimating your aerobic capacity based on years of research, a complicated equation or two and some generalizations that may not fit you exactly. You may have a higher resting and/or exercising heart rate than the “average” person.

Theoretically, your maximum heart rate can be determined with the equation 220 minus your age (e.g 220 – 40 yrs. = 180 beats per minute). This number, your maximum heart rate (HRmax), is then used to calculate the ideal heart rate range for you to stay within while you exercise, called your target heart rate range (THR).

You will often hear that one should exercise between 70-85% of his/her HRmax (e.g. for the 40 yr old above, that would be 126-153 bpm). However, these numbers can vary from individual to individual based on each person’s true maximum heart rate.

The HRmax as determined by the (220 - your age) equation is purely an average and can, in fact, vary by as much as 12 beats per minute either way. As a 40 yr. old, you may find that you have a maximum heart rate closer to 190 or perhaps as low as 170. Thus, your THR zone may be as high as133-162 or as low as 119-145 bpm.

If you fall into one of these outlying categories, the fit test on your treadmill may provide an inaccurate estimate of your aerobic capacity.

Even in this example, fitness testing can still be a valuable tool to measure the progress you’re making with your exercise program. This week, the test gave you a 40. Do it again in a couple of months and see what happens.

If the number is going up, you’re headed in the right direction. If not, perhaps you need to make an adjustment in your exercise program to better challenge your cardiovascular system. Or, a declining number can signal over-training and you may need to simply give your body a rest for a few days rather than ramp up the workout.

Fitness testing can be a great way to motivate you to exercise and to exercise at gradually greater intensities for better results. It may only be an estimate but it should be a consistent estimate and one you can use to measure your progress over time. I hope I answered your question somewhere in there.

Good luck and keep moving!

[Dan Strayton, general manager at Health Unlimited on Century Drive in Mt. Airy, holds a master's degree in exercise physiology and would be happy to answer any questions you may have about exercise, health and fitness. Write to him in care of the Mt. Airy Messenger, P.O. Box 897, Mt. Airy, MD 21771‑0897; or send e-mail to dans@myhealthunlimited.com.]