What is a Graded Exercise Test (GXT)? What are the benefits?

A Graded Exercise Test (GXT) is a tool used by exercise professionals to assess your heart health and fitness. It measures how well your heart, lungs, and muscles respond to a gradually increasing exercise intensity.

This test provides super in-depth information that allows us to get an accurate reading of cardiovascular fitness, diagnose heart conditions, and guide specific exercise prescriptions.

If you are about to go for a GXT, here is everything you need to know.

Graded Exercise Test setup with treadmill and monitoring devices

What does a GXT consist of?

The GXT can be performed on either a stationary bike or a treadmill. You will slowly increase the intensity of your exercise until the completion of the test. Your medical professional will provide all the instructions on the day.

Before beginning a GXT, you will first be introduced to multiple measurement devices.

Depending on the purpose of the test, these usually consist of:

• an electrocardiogram (ECG) - which is where dots will be put on your chest which allow the electrical activity of the heart to be monitored.

• Blood pressure monitor - a wrap that goes around your upper arm and inflates to measure the pressure of your blood.

• A mask to measure breathing - this will measure the oxygen and carbon dioxide you are inhaling and exhaling which will show which energy system you are using. Sometimes you will need to put on a nose peg to breath only through the mask.

• A chart of your exertion level (RPE) - this is to measure how hard you feel you are working

These devices will take a few minutes to set up, and to get some measurements at rest.

Sometimes you will be asked to complete a lung assessment beforehand, which consists of blowing into a tube attached to a machine. This can help diagnose conditions such as asthma and chronic obstructive pulmonary disease (COPD).

A GXT can be performed maximally or sub-maximally - both of which you will cease exercise at a certain predetermined intensity. Maximal tests provide more accurate data, but sub-maximal can be useful for estimating fitness without pushing your body too hard.

A professional will be monitoring your vital signs throughout the whole test, and may stop the test early if necessary, making a GXT a very safe form of exercise.

How the Test Is Conducted

The goal of this test is to observe how the cardiovascular system responds to stress. By increasing the workload step-by-step, the test can reveal abnormalities that might not appear at rest.

The procedure usually starts with a warm-up at a low intensity. Then, every few minutes, the workload increases by raising the treadmill speed or incline or increasing the resistance on a bike. You will be asked to continue until you reach a predetermined endpoint, or the medical professional asks you to stop. You may stop the test at any time.

Why is the GXT important?

The GXT provides valuable information that cannot be obtained from resting measurements alone. Here are some key reasons why this test is so important:

Detecting Heart Disease

Some heart problems only show up during physical stress. The GXT can identify:

• Coronary artery disease by triggering symptoms

• Arrhythmias triggered by exercise

• Abnormal blood pressure responses

These can be used to guide treatment, leading to better health outcomes.

Assessing Physical Fitness

A GXT is the gold standard for measuring VO2MAX which is the most accurate measure of cardiovascular fitness. It also provides data on what specific intensities will work different energy systems - which can be a powerful tool for prescribing exercise intensity accurately for athletes or patients.

Guiding Rehabilitation

For patients recovering from health conditions such as a heart attack, the GXT helps exercise physiologists design safe exercise plans. It shows exactly what intensity of exercise is safe to perform, which is a big barrier to these patients returning to their previous lifestyle.

Evaluating Symptoms

When patients have unexplained chest pain, shortness of breath, or fatigue, a GXT can help determine what the limiting factor is. Is it the heart, the lungs or something else?

Before completing the GXT:

• Avoid heavy meals right before the test

• Avoid caffeine and smoking for a few hours before the test as they can alter your heart rate

• Wear comfortable clothing and shoes suitable for exercise

• Be aware the mask is not always comfortable, some people find it triggers their claustrophobia. If you believe this may be a problem, mention it as soon as you can.

• Inform the medical team about medications, as some can affect heart rate or blood pressure

  
  

What Happens After the Test?

After the GXT, the healthcare team reviews the data collected. They will often not be able to give a full summary immediately following the session as there is a lot of data to collect, this may take a few days to complete. Based on findings, they may:

• Recommend lifestyle changes or medications

• Suggest further tests

• Develop personalised exercise programs

• Monitor progress with repeat testing

  
  

Risks and Safety Considerations

While the GXT is safe, all exercise comes with a certain level of risk. Medical supervision and emergency equipment are always present during the test. To minimise risk your medical team will always:

• Screen for contraindications before testing

• Stop the test immediately if dangerous symptoms occur

• Monitor your vital signs continuously

  
  

In very rare cases (this study shows a rate of only 0.16% in people with high risk cardiovascular disease), it can cause an adverse event such as ventricular tachycardia. If a complication does arise the test is stopped and you will be in a safe, medically trained location.

Real-Life example of a GXT and why it's important

The following is a real patient story that I have seen in my career:

After being diagnosed with stomach cancer, a 65 year old man requires a major surgery to remove it. This surgery requires deflating 1 lung for at least 8 hours and a number of weeks in hospital recovering afterwards. The patient also has a long-standing heart condition. The surgeon requests a GXT to measure the patient's fitness for surgery. The test finds a VO2MAX below the required threshold, and therefore surgery cannot be performed. An exercise physiologist (that was me!) creates a specific high intensity interval program using a percentage of maximum heart rate from the test that is safe for the patient's heart and effective so he can have the surgery as soon as possible. The test is repeated 4 weeks later to confirm the patient has improved their fitness enough to survive the surgery and the patient gets his life-saving treatment.

Summary

The GXT is a powerful diagnostic tool for exercise professionals. It assesses cardiovascular health and fitness by measuring how the heart, lungs, and muscles respond to increasing exercise intensity while under medical supervision. Using tools such as ECG, blood pressure monitors and breathe analysis, it provides detailed data that is essential for detecting health conditions, guiding treatment and prescribing exercise. It is a safe, closely monitored test that can be very important in guiding your treatment.

So be prepared to work hard to get the most accurate results for your treatment, and as always...

Stay Strong!