Assessing your fitness level
By the faculty of Harvard Medical School for The Harvard Medical School Adviser

Q: I've started a powerwalking program to get in better shape. How can I tell if I'm actually improving my fitness level?

A: Congratulations on starting an exercise program, which can help you live a longer and healthier life. One of the most important benefits of aerobic exercise (like waking) is to your cardiovascular system: your heart, your blood vessels and the muscles that take up oxygen from the blood to power physical activity. Also known as aerobic fitness, cardiovascular fitness is a measure of how well those organs work -- and work together.

The most accurate test of aerobic fitness is called the VO2 max. It's similar to an exercise stress test done by cardiologists to check how well your heart performs under stress. The test measures the amount or volume (V) of oxygen (O2) that you use when you exercise as hard as you can. You ride on an exercise bike or walk or run on a treadmill, increasing speed and difficulty until you're too exhausted to continue. It's done in an exercise or cardiac stress test lab, under close medical supervision. During the test, the air you exhale is analyzed to calculate your VO2 max. Similar but less precise measures of aerobic fitness can also be done in a doctor's office or at a health club.

But you don't necessarily need such an elaborate test to gauge your fitness. Instead, you can do a simple walking test, called the Cooper 12-minute fitness test. Go to a track and see how far you get in 12 minutes, walking or running or both. Each lap around a standard track is one-quarter of a mile. Then rate yourself as follows: Poor to fair for less than 0.5 mile; good for 0.5-1 mile; very good for 1-1.5 miles; and excellent if you make it more than 1.5 miles. Although it's not as precise as the VO2 max, the Cooper test is still a pretty good indicator of physical fitness. Its main limitations are that it doesn't give an accurate picture if you have bone, joint, or muscle problems that make walking or running difficult, and it doesn't make allowances for age or gender.

To boost your aerobic fitness, you can do any exercise that raises your heart rate and makes you breathe faster -- brisk walking, swimming, cycling or aerobics, for example. The aerobic doctrine calls for you to work out at 70 percent to 85 percent of your maximum heart rate for 20 to 60 minutes on three to seven days each week. (To calculate your maximum heart rate, subtract your age from 220.) A good rule of thumb is that if you can talk easily while exercising, you need to work harder. On the other hand, if you can't carry on a conversation at all, ease up a bit. Aim for 30 minutes or more on most days. It's fine to reach that total by way of 10- to 15-minute periods.

Recent evidence suggests that more moderate exercise is enough to improve both cardiovascular risk factors and overall health, even without a major boost of your VO2 max. So if pushing yourself with a power walk turns exercise into a chore, consider using moderate exercise such as intense walking, gardening, stair climbing or household chores to earn the health benefits listed in the graphic. (For more information, see The No Sweat Exercise Plan: Lose Weight, Get Healthy, and Live Longer, a Harvard Medical School Book by Harvey B. Simon, MD, McGraw-Hill, 2005).

Skeptics might ask, "Why bother with all the huffing and puffing?" For some, the answer is a more vigorous, active, athletic life. For others, it is a healthier life with heart disease. Low cardiorespiratory fitness is a strong predictor of premature death. It's on the same level as smoking, high blood pressure, obesity and diabetes. What's more, poor cardiorespiratory fitness can worsen the effects of other risk factors. For example, low cardiovascular fitness raises the risk that a person with normal blood pressure will develop hypertension in the next five years. New data estimate that 50-year-olds with high levels of physical activity live 3.5 to 3.7 years longer than those with low physical activity. Virtually all of the extra years are healthy ones free of cardiovascular disease. In other words, a daily workout could add four healthy years to your life.

Copyright 2006 the President and Fellows of Harvard C o l l e g e . Developed by Harvard Health Publications (www.health.harvard.ed u). Distributed by UFS. Submit questions to harvard_ adviser@hms.harva rd.edu.