What Is an Exercise Tolerance Test?

An exercise tolerance test (also called a stress test) shows how well your heart handles physical activity. While exercising on a treadmill or stationary bike, a healthcare provider will measure your heart rate, blood pressure, and breathing while monitoring an electrocardiogram (ECG), a test that records your heart's electrical signals.

Exercise tolerance tests are generally used to detect certain heart conditions or determine safe levels of exercise for people with existing heart conditions.

This article provides an overview on what an exercise tolerance test entails and how to understand the test's results.

Purpose of an Exercise Tolerance Test

Exercise tolerance tests evaluate how hard your heart works when it’s under the stress of physical activity.

When we exercise, our hearts pump harder and faster to deliver blood and oxygen throughout the body. It’s often easier to detect certain heart conditions while your heart is working hard, since the heart may appear to be working normally while at rest.

After hooking a patient up to a blood pressure cuff and ECG during exercise on a treadmill or stationary bike, healthcare providers can monitor your:

• Heart rate
• Blood pressure
• Breathing
• Level of exertion

Not everyone needs an exercise tolerance test. They’re mainly used to detect a heart condition or monitor a preexisting heart condition. For example, a healthcare provider may recommend this test:

• If you have symptoms like chest pain or shortness of breath that could indicate a heart condition
• If you have an irregular heartbeat
• To determine a safe exercise plan for patients recovering from heart surgery
• To see if treatments you’re receiving for heart disease are working well

Limitations of an Exercise Tolerance Test

As with any medical test, exercise tolerance tests have some limitations. For example:

• Exercise tolerance tests can help detect an artery blockage in coronary artery disease, but they can't predict things like how much of the artery has thickened or if and when a person may have a heart attack.
• Exercise tolerance test results aren't always 100% accurate and can vary based on equipment used, experience of the healthcare professional conducting the test, and other factors. Some people may get a false-positive result, indicating a heart condition when there is none.

With this in mind, your healthcare provider will typically use the results of an exercise tolerance test along with other information, like your symptoms, medical history, and results of other tests, to make a determination or diagnosis.

Risks of an Exercise Tolerance Test

An exercise tolerance test is a relatively safe test.

That said, sometimes increasing your heart rate through exercise can cause symptoms like dizziness, chest pain, or nausea. A healthcare provider will closely monitor you throughout the test to reduce the chances of this happening and quickly treat any issues that may come up.

In addition, people with certain preexisting heart disease can experience complications like an irregular heartbeat or even a heart attack. To be safe, your healthcare provider would likely not recommend an exercise tolerance test if you have any of the following heart conditions:

• Unstable angina (chest discomfort caused by poor blood flow)
• Uncontrolled arrhythmia (an irregular heartbeat)
• Pulmonary hypertension (a type of high blood pressure)
• Severe aortic stenosis (narrowing of the main artery)
• Congestive heart failure (a condition in which the heart doesn't pump blood as well as it should)
• Pulmonary embolism (a clot in the arteries of a lung)
• Aortic dissection (a tear in the main artery)
• Another acute illness

Before the Test

There’s not much preparation needed for an exercise tolerance test. Your healthcare provider will give you a set of guidelines to follow, which may include these instructions:

• Avoid eating a heavy meal or consuming anything other than water within a few hours of the test.
• Avoid consuming caffeine the day before the test.
• Wear loose-fitting clothing and comfortable walking shoes.
• Continue to take any usual medication unless otherwise advised by a healthcare provider.

During the Test

Exercise tolerance tests take place at a healthcare provider's office or at a hospital and will be overseen by a medical professional. They are relatively quick and painless, minus any potential minor discomfort felt while exercising. The test itself should take about 15–20 minutes. 

Here's what you can expect:

1. Equipment used will include a treadmill or exercise bike, ECG machine connected to electrodes (wires), a blood pressure cuff, and a pulse oximeter to measure blood oxygen levels.
2. The small electrodes will be stuck to the skin of your chest or shoulders and attached to the ECG machine to measure your heartbeat and heart waves. In addition, the blood pressure cuff will be wrapped around your arm, and the pulse oximeter sensor will be clipped to your finger. 
3. You’ll then be asked to start exercising on the treadmill or bike at an easy pace. Gradually, the speed and incline are increased while the ECG monitors your body and heart’s reaction to the stress of exercise.
4. You may be asked to breathe into a mouthpiece that will measure how much air you're breathing out.

Before, during, and after the test, your ECG, heart rate, blood pressure, and breathing will be monitored and recorded.

After the Test

When the test is done, you’ll be able to sit or lie down for several minutes until your heart rate returns to its normal resting state. You may be offered a glass of water or towel while you cool down.

If your blood pressure substantially rose during the test, or if the healthcare provider noticed any other concerning symptoms, you may be monitored for a few additional minutes.

After getting clearance, you'll be free to return home and await the test results, which usually come back within a couple of days.

Interpreting Results of an Exercise Tolerance Test

After the test is performed, your healthcare provider will look over the results. They’ll be evaluating factors like:

• Your ECG reading
• Blood pressure changes
• Heartbeat changes
• Any symptoms reported or noted during the test
• Your estimated exercise capacity 

After summarizing these items, your provider will go over the results with you and offer a conclusion based on their interpretation. Possible results include:

• Positive (or abnormal): This means the test found potential evidence of a heart condition.
• Negative (or normal): This means the test didn't find any evidence of a heart condition.
• Inconclusive or uninterpretable: This indicates the test was unable to determine if a heart condition is present. In this case, the equipment may have malfunctioned, or you were unable to complete the test.
• Goal achieved: If you took the test to help establish a safe exercise plan following a heart diagnosis or surgery, your healthcare provider might have set some fitness goals that you were able to meet.

Follow-Up

Depending on the results, your healthcare provider may want to speak with you about further testing, alternative testing, or treatment options.

In some cases, more appointments or testing may be necessary to:

• Confirm your exercise tolerance test result
• Seek additional information after your exercise tolerance test result

Follow-up tests may include:

• MRI (magnetic resonance imaging) heart scan to evaluate the structure of your heart
• CT coronary scan to look at the arteries that supply blood to your heart
• Myocardial perfusion scan to provide a visual on how well the heart is pumping
• Nuclear stress test to measure the blood flow to your heart
  

Summary

An exercise tolerance test is one way to record your heart's response to the stress of physical exercise. It measures the heart's electrical activity, heart rate, blood pressure, and breathing while you're on a treadmill or exercise bike.

Exercise tolerance tests may be used to diagnose certain heart conditions, monitor heart attack recovery, or form an appropriate fitness plan for heart disease or surgery patients. Your healthcare provider may recommend this test if you report symptoms of potential heart disease, such as chest pain or shortness of breath. This test generally isn't recommended for people at low risk of developing heart disease.

A Word From Verywell

An exercise tolerance test is one tool to help diagnose certain types of heart disease and monitor existing heart conditions, but it isn't the only one available. If you're experiencing symptoms that you think may be heart related, or if you've had an exercise tolerance test but don't understand the results, reach out to a healthcare provider for help or a second opinion.

Check out the American Heart Association website for a list of helpful questions to ask your healthcare provider, as well as other resources for patients seeking assistance.