Cardio Fitness: Vital Sign of Heart Disease Risk


Regular exercise is good for your heart. It’s a refrain often heard, but not always heeded. Now comes word that having your doctor measure your aerobic fitness level is as essential as taking your pulse when determining your heart health.

Late in 2016, the American Heart Association (AHA) issued a statement recommending, at a minimum, routine fitness estimations for all adults. The statement, based on a review of available data, went so far as to describe cardiorespiratory (or aerobic) fitness as a vital sign, giving it the same importance as heart rate, body temperature, respiration rate, and blood pressure reading for evaluating overall health.

Research is finding that a person’s fitness level can be a more powerful predictor of disease risk- and death-than such traditional risk factors as hypertension, smoking, obesity, high cholesterol, and type 2 diabetes.

Despite the clinical evidence, doctors don’t routinely assess cardiorespiratory fitness, according to the statement.

Why fitness matters

Cardiorespiratory fitness refers to the body’s ability to efficiently deliver oxygen to working muscles. High fitness levels are a marker that the heart, lungs, and blood vessels are functioning well. Low fitness levels, in contrast, can indicate dysfunction in the body.

Over the years, many studies have linked low fitness levels to an increased risk of death from any cause, and from heart disease in particular. That doesn’t apply only to people who are less active because they’re in poor health. Fitness matters over and above other factors.

A study published in Mayo Clinic Proceedings in 2017 offers a case in point. It involved more than 20,000 U.S. veterans with an average age of 58 who were free of heart disease at the outset. All underwent fitness testing by walking on a treadmill and then had their health tracked over a median period of 11 years.

Overall, the study found that the higher the veterans’ fitness levels, the lower their risk of suffering a heart attack, heart failure, or a stroke-even when the researchers accounted for other factors, such as older age, obesity, smoking, type 2 diabetes, high blood pressure, and high cholesterol. The findings suggest that fitness itself has an impact.

An important point: It did not take high fitness levels for people to benefit. Those with a modest fitness level were 29 percent less likely to develop heart disease or stroke than the least-fit study participants. Modest fitness translates into a realistic goal that most middle-aged and older adults can achieve through regular moderate exercise, such as brisk walking.

Many studies suggest that even incremental improvements in fitness can contribute to a healthier heart and longer life. The reasons are numerous. For one, regular exercise helps control heart disease risk factors like high blood pressure, excess body fat, and type 2 diabetes. People who are fit also tend to have better-functioning blood vessels and improved autonomic nervous system tone, which may help ward off a heart attack or arrhythmias. The autonomic nervous system regulates the activity of heart muscle.

Measuring fitness

Despite the evidence, doctors have not traditionally considered fitness when estimating patients’ risk of developing heart disease. That’s partly because, for a long time, it was not clear that fitness testing added much information to standard measures of heart health, such as blood pressure and cholesterol levels.

Furthermore, fitness testing can be time-consuming and impractical. The most accurate approaches require trained personnel and expensive equipment not usually found in the offices of primary care doctors.

But the AHA says there is now enough convincing evidence that fitness estimates based on reported exercise routines are worthwhile. And although a fullscale exercise test is not cost effective, there are simpler ways to reliably measure fitness. Testing options include:

The gold standard. The gold standard. Ideally, fitness is measured with cardiopulmonary exercise testing. This is done using a special treadmill (or sometimes a stationary bike) with equipment that allows your doctor to monitor not only your heart rate and blood pressure as you exercise, but also your oxygen use. This type of testing is the best measurement of cardiorespiratory fitness, because it directly records the peak level of oxygen you’re using as you move. However, this testing is too expensive and time consuming to perform clinically in an asymptomatic person.

Next best options. If cardiopulmonary testing is not available, your doctor may order a standard exercise tolerance test, which most often entails walking on a treadmill. There is no direct measurement of your breathing, but often your fitness level can be estimated based on the speed, intensity, and duration that you’re able to achieve.

If treadmill testing is not available, or you have physical limitations that make it difficult, alternatives are available. One is the six-minute walk test, which measures the distance you’re able to walk on a flat surface in six minutes.

Exercise-free estimate. If exercise testing cannot be done at all, your doctor may use some basic information to assess your fitness. Your age, sex, exercise habits, resting heart rate, and waist size, for example, can be inserted into a standard equation that estimates your fitness level.

How exactly is “fit” defined? Fitness is typically expressed in metabolic equivalents, or METs. A MET is the ratio of the rate of energy expended during an activity to the rate of energy expended at rest. There are no clear thresholds that separate the fit from the out-of-shape. But according to the AHA, fitness levels at or below 9 METs-considered relatively low-have been linked to increased heart risks.

Boost your fitness

Fortunately, people of all ages can increase their fitness levels. Research has shown that each 1 MET increase in cardiorespiratory fitness, a small increment achievable by most people, is associated with a 10 to 25 percent increase in longevity-meaning a longer life. The standard advice you’ve heard for years-moderate exercise on most days of the week-will do the job for most people.

It’s also important to note that studies have consistently shown that the greatest health benefits occur when the least-fit individuals progress into the next least-fit group. The AHA statement called this an often misunderstood but important public health message, because a person does not need to be athletic to gain substantial health benefits from improvements in cardiorespiratory fitness.

Age itself is not a critical factor in creating an exercise plan. It depends more on your current fitness level and personal preferences. If you are sedentary or have a relatively low fitness level, it will not take much exercise to see a positive change. Studies show that brisk walking, even for three to four times a week, can lead to meaningful improvements in fitness.

Ideally, walking and other moderate-level activities should be sustained for 30 minutes to an hour. Sedentary people can start with 10 to 20 minutes, which is enough to boost their fitness levels-and, in turn, allow them to gradually increase their exercise time. Even if you’re already fairly fit (in the 9-14 METs range), you don’t have to go all out to see improvements: Fast-paced walking is a good choice, as is slow jogging, hiking, or bicycling.

If none of these options appeals to you, select any activity that gets you moving over a sustained time and ups your heart rate. This could include swimming, dancing, or rowing, for example.

Choosing activities that you actually enjoy is important, because you will need to do them regularly. If you’re exercising at a moderate-intensity level, you should be active five days a week-or gradually build up to that. If higher-intensity workouts (such as running) are appropriate for you, three days a week will suffice.

The bottom line

If your doctor has not gauged your fitness level in some way, ask him or her about it. You can also try using a scientifically validated online tool, such as the one at It calculates your estimated peak oxygen consumption during exercise and tells you whether your fitness level is high, low, or typical for your age. You can bring the information to your next doctor appointment and discuss what it might mean for your heart health.

In general, a daily walk is a safe activity for most people. But if you have always been sedentary, or have any chronic health conditions, it is always wise to talk with your doctor before starting a new exercise routine.