In a stress test — also known as an exercise or treadmill test — a doctor monitors a person’s heart rate as they exercise or undergo a chemical stressor.

It can show how well a person’s heart works during physical activity and help diagnose various heart conditions.

A stress test typically involves walking on a treadmill or using a stationary cycle while medical devices monitor breathing, blood pressure, heart rate, and heart rhythm.

Some people, such as those with arthritis, may not be able to do the activities involved in an exercise stress test. Instead, a doctor will give these people a drug to make their heart work harder, as it might during exercise.

In this article, learn why a doctor may recommend a stress test and what to expect during one.

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There are a few different ways of completing a stress test, depending on the person’s needs.

Exercise stress test

During a stress test, the doctor will aim to determine the person’s heart rate, blood pressure, breathing, and how tired they feel during different levels of physical activity.

According to the American Heart Association (AHA), during a stress test using a treadmill:

  1. A doctor attaches sticky electrodes to the person’s chest to monitor the heart, then they will take some readings.
  2. Next, the person will stand on the treadmill.
  3. As the treadmill starts to move, the person will walk slowly.
  4. The treadmill speed will gradually increase.
  5. The treadmill may go into an uphill, or incline, position.
  6. Toward the end, the person may breathe into a mouthpiece to measure the air they breathe out.
  7. The treadmill will stop, and the person will lie down while the doctor takes their blood pressure and other readings.

The person will exercise for 10–15 minutes but can ask to stop at any time if they feel unwell.

If the person experiences any of the following, the doctor might stop the test:

They may also stop the test if the electrocardiogram (EKG) or echocardiogram device detects any unusual changes.

Stress test without exercise

According to the AHA, if a person cannot exercise, the doctor may use a certain medication to trigger the same process.

In this case, they will attach electrodes to the person’s chest and deliver the medication into their arm through an intravenous (IV) line.

The medication will stimulate the heart. It may cause effects similar to those that occur during exercise, such as flushing or shortness of breath.

Nuclear stress test

Depending on the results, the doctor may recommend a nuclear stress test as a next step.

Also known as a nuclear heart test or radionuclide scan, this can give a more detailed and accurate assessment of the heart.

The process is similar to that of the exercise stress test, but the doctor will inject a tracer dye into the arm to highlight the heart and blood flow on an image. The dye will also show any areas of the heart where blood is not flowing. This can suggest a blockage.

As with the exercise test, if a person cannot exercise, the doctor may use medication instead.

The person will then undergo an imaging test that involves a small amount of radiation, such as a single-photon emission computer tomography or cardiac PET test.

The doctor will take two sets of images, each covering 15–30 minutes. They will take the first just after the person has exercised and the second when their body is at rest, either later that day or the next day. They may also take “at rest” images before the person exercises.

In this way, the doctor can compare how the heart looks and functions normally and while under stress.

This test is not suitable for anyone who is or may be pregnant, as radiation may harm the fetus. Anyone who is breastfeeding should let the doctor know beforehand.

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A doctor may advise the person not to consume caffeinated drinks or take certain medications on the day of the test. These substances could affect the results.

Anyone who usually has an inhaler should bring it to the test and ensure that the doctor knows about it.

Exercise stress test

A person should wear comfortable clothes and walking shoes.

The test involves the doctor hooking the person up to various medical devices that monitor the heart. To achieve this, the doctor will place:

  • sticky patches, or electrodes, on the chest
  • a blood pressure cuff around the arm
  • a pulse monitor on the finger

A healthcare professional may need to shave a person’s chest to allow the electrode patches to stick.

If the person is not exercising, they will receive an infusion of a certain medication into their arm through an IV line. This may cause side effects.

Nuclear stress test

A person should avoid applying oil, lotion, or cream to their skin on the day of the nuclear stress test.

The doctor will give the person an injection of the tracer liquid. This may feel cold. The technician will take some images of the heart before exercising and after. A person lies flat on a table for these images.

The length of time spent exercising will depend on how often a person exercises and their medical history. The test may take a couple of hours.

What the doctor is monitoring

Some factors the doctor will aim to measure include:

  • heart rate
  • breathing
  • blood pressure
  • EKG readings or imaging results
  • how exercise affects fatigue levels
  • heartbeat and heart waves

Possible results of the exercise stress test include:

  • normal blood flow during exercise and rest
  • normal blood flow when resting but not during exercise, possibly indicating a blocked artery
  • low blood flow when exercising and resting, suggesting coronary artery disease
  • no dye in some parts of the heart, implying tissue damage

During the test, doctors may ask people to exercise at 85% of their maximum heart rate. They usually determine the maximum heart rate by subtracting the person’s age from 220. If a person’s actual heart rate exceeds their “maximum,” the doctor may ask them to stop exercising.

If a person does not reach their target heart rate, this may indicate they have a heart problem.

Doctors may look at how well a person’s heart rate recovers after exercise. To measure this, they can subtract the heart rate one minute after exercise from the peak heart rate. If a person’s heart rate has dropped significantly, they have shown an easy recovery.

Peak heart rate minus heart rate 1 minute after intense exercisePerformance
less than 12 beats per minute (bpm) in a walking recoveryabnormal
more than 12 bpm in a walking recoverynormal
less than 18 bpm in recovery lying on backabnormal
more than 18 bpm in recovery lying on backnormal

Sometimes doctors measure stress test results in metabolic equivalents or METS. These tell the doctor how well a person tolerates exercise. METS equate to oxygen uptake in milligrams, measured per kilogram per minute. This is a less exact measurement and depends on how doctors conduct the test.

under 5 METS or inability to exercise for 6 minutes or raise the heart rate to 85% of maximumpoor
5–8 METSfair
9–11 METSgood
12 METS or moreexcellent, any score above 10 METS suggests a 5-year survival rate of 95%

If the results of the stress test raise no concerns, the person will need no further tests.

If the results are unclear or suggest that damage is present, the doctor may recommend further tests or treatment.

Stress tests can help a doctor diagnose various heart conditions. They can also help identify a person’s risk before undergoing an activity that may put a strain on their heart and show how well a person’s heart handles a workload.

A doctor may recommend a stress test if a person has symptoms that could indicate a heart condition, such as:

A doctor may also recommend a stress test if a person:

  • is undergoing heart treatment
  • is due to have heart surgery
  • is due to have another type of surgery
  • is considering starting a vigorous exercise program

When the heart pumps harder during exercise, the stress test can reveal issues such as low blood supply through the coronary arteries. These problems might not be apparent at other times.

Both the exercise stress test and the nuclear stress test are usually safe.

In rare cases, however, they could trigger adverse effects. These include a heart attack or changes in heart rhythm that do not disappear after the test.

Statistics suggest that this happens in around 1 in 10,000 cases. For this reason, doctors do not recommend this test unless a person meets certain criteria.

A person should not undergo an exercise stress test if they:

People who are pregnant should not undergo certain stress tests.

Exercise stress test

Medical professionals typically do not recommend exercise stress tests during pregnancy, as they believe the risks outweigh the benefits. This is because pregnancy puts the cardiovascular system under additional pressure. However, in an older 2005 study researchers safely conducted exercise stress tests up to 38 weeks of gestation .

Pregnant people should not undergo a nuclear stress test since it is harmful to a developing fetus.

Healthcare professionals do not typically recommend imaging tests that use ionizing radiation, such as PET scans, for pregnant people. However, in some cases, they may deem an imaging test clinically necessary. In these cases, they will discuss the possible risks and benefits with the pregnant person and use lowest effective dose of ionizing radiation during the scan.

Scientists have linked some pregnancy complications to a higher risk of cardiovascular disease. These include:

To screen for possible cardiovascular risks, doctors may use the following:

  • exercise stress test
  • isometric handgrip test
  • cold pressor test

The pros of conducting an exercise stress test during pregnancy are that they can be a helpful indicator of fitness, and testing in the first trimester can help predict risks later in pregnancy.

The cons are that the test can be stressful for a pregnant person, they may require the use of a recumbent bicycle or other special equipment, and it can be tricky to determine how intense the exercise should be.

More research is needed to investigate whether the findings from an exercise stress test are worth the risks.

A stress test can show how well the heart is working and help diagnose various heart conditions.

It can also give an idea of how much strain a person’s heart can cope with. This can be helpful when planning for heart surgery or a vigorous exercise program.

The test usually involves walking on a treadmill while a doctor monitors heart activity. However, people with reduced mobility may need to receive a certain medication to produce a similar effect.

A stress test can give an idea of a person’s heart health and guide recommendations on exercise and other forms of therapy.

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