Stress test: what the heart reveals when the body needs to perform
Many cardiovascular problems do not manifest themselves when a person is sitting, calm or at rest. They may occur when walking uphill, walking briskly, resuming sporting activity, carrying a heavy load, climbing stairs or performing an activity that used to be routine but which suddenly begins to cause fatigue, chest tightness, palpitations, shortness of breath or a slower-than-expected recovery.
This difference between rest and exertion is one of the key aspects of functional cardiological assessment. The heart does not behave in the same way when the body is at rest as when it needs to respond to physical demands. At rest, the body requires a relatively stable amount of oxygen and energy. During exercise, however, the muscles need a greater blood supply, the heart rate increases, blood pressure adjusts, and the cardiovascular system must work harder to maintain balance.
The stress test allows us to study precisely this response. It is not just a matter of observing the heart, but of seeing how it behaves when the body demands more of it.
As Dr Felipe Hernández Hernández, a cardiologist and head of the cardiology department at the Publio Cordón Memorial Hospital, explains, “the stress test, or ergometry, is a test we carry out in cardiology to assess various aspects of the patient’s condition. We are interested in assessing functional capacity, that is, the duration of exercise a person can perform whilst walking, although it can also be carried out on a bicycle”.
That definition summarises the basic concept, but it is worth going further. A stress test is neither a sporting event nor an isolated measurement of physical endurance. It is a medical examination that allows us to analyse how the heart responds when the body’s demands gradually increase.
What is a stress test?
A stress test, also known as ergometry, is a cardiological examination that studies the response of the cardiovascular system during controlled physical exercise. It is usually carried out by walking on a treadmill, although in certain cases it can be done on a stationary bike. The choice depends on the patient’s characteristics, their physical capacity and the clinical question the cardiologist needs to answer.
During the test, the patient performs progressively more strenuous exercise whilst the medical team records various parameters. The electrocardiogram is monitored, the heart rate is checked, blood pressure is measured at regular intervals, and the team observes whether symptoms such as chest pain, shortness of breath, dizziness, palpitations or disproportionate fatigue occur.
Dr Hernández Hernández explains this from a clinical perspective: “During this test, the heart rhythm is monitored. We have a screen displaying the electrocardiogram so we can view the trace and detect any abnormalities; in addition, the patient’s blood pressure is also taken at regular intervals.”
This monitoring allows us to observe changes that do not always appear during a resting assessment. The test is not intended to exert the patient unnecessarily, but rather to simulate a situation of physical exertion in a controlled environment, under medical supervision and with clear criteria for adapting or stopping the exercise when necessary. The American Heart Association’s standards for exercise testing emphasise precisely the importance of selecting the appropriate protocol, monitoring the clinical and electrocardiographic response, and interpreting the results within the context of each individual patient.
Why exercise provides different information
One of the most common questions is why it is necessary to walk, cycle or raise one’s heart rate to assess cardiovascular health. The answer lies in physiology: the heart needs to work harder when the body is moving.
At rest, the heart muscle consumes less energy and requires a relatively stable blood supply. During exercise, however, it must pump with greater force and at a higher rate to ensure oxygen reaches the muscles and the rest of the body. This increased demand also means that the coronary arteries, which are responsible for supplying blood to the heart itself, must respond appropriately.
Dr Hernández Hernández sums it up clearly: “At rest, the heart doesn’t really use much energy or need too much blood. But physical exercise speeds up the heart rate so that blood reaches all parts of the body, and that causes its workload to increase significantly.”
This is why certain abnormalities may remain undetected at rest but become apparent during exercise. If the blood supply to the heart does not increase sufficiently, if an exercise-induced arrhythmia occurs, or if blood pressure responds abnormally, the test can provide relevant clues to guide the diagnosis.
Put simply, the stress test allows us to ask a very specific clinical question: does the heart respond as expected when the body needs to work harder?
How the test is carried out
Before starting, the medical team reviews the patient’s medical history, background, symptoms, regular medication, level of physical activity and the purpose of the test. This preliminary assessment is important because not everyone requires the same protocol or the same intensity of exercise.
Electrodes are then placed on the chest to record the electrocardiogram throughout the test. A cuff is also used to measure blood pressure at various points. Once the patient is ready, the exercise begins at a low intensity and is gradually increased. On the treadmill, this is usually done by increasing the speed and incline; on the exercise bike, by increasing the resistance.
The patient is supervised and monitored throughout the process. The test may be stopped when the target is reached, when the patient becomes sufficiently fatigued, if symptoms arise that warrant stopping it, or when the cardiologist considers that the necessary information has been obtained. This is followed by a recovery phase, during which the heart rate and blood pressure are monitored as they return to normal, and it is noted whether any symptoms subside.
This subsequent phase also provides valuable information. It is not only important how the heart responds when the workload increases, but also how it returns to normal once the test is over. The ACC/AHA guidelines on stress testing and the American Heart Association’s standards emphasise the importance of assessing both the exercise phase and the recovery phase, as both can provide relevant clinical information.
What the cardiologist is really looking for
One of the most important points to clarify is that a stress test is not interpreted solely on the basis of how long a person manages to walk or cycle. The duration achieved forms part of the information, but it is not the only piece of data, nor is it necessarily the most important.
As Dr Hernández Hernández states, “we are not so much looking at the duration of exercise, but rather at the heart’s response to physical activity and determining whether there are any abnormalities or signs suggesting an underlying heart problem”.
During the test, the cardiologist analyses the electrocardiogram, heart rate, blood pressure, symptoms and recovery. They also assess whether the patient’s functional capacity is in line with what would be expected given their age, physical condition and clinical status.
This concept has become increasingly important in cardiovascular medicine. In 2016, a scientific statement from the American Heart Association argued that cardiorespiratory fitness should be considered a true clinical ‘vital sign’. The document reviewed the accumulated evidence and concluded that low levels of cardiorespiratory fitness are consistently associated with an increased risk of cardiovascular disease, all-cause mortality and poorer health outcomes.
This does not mean that everyone should undergo a stress test, nor that a single result can predict the future. It means that, where there is an appropriate medical indication, measuring how the body responds to exercise can provide additional information that cannot be obtained simply by observing the patient at rest.
What a stress test can detect or assess
The exercise stress test has traditionally been used to investigate possible signs of exercise-induced myocardial ischaemia. Ischaemia occurs when the heart muscle does not receive sufficient blood and oxygen to meet its current demand. This may be related to coronary artery disease, although it must always be interpreted within the context of the patient’s full clinical history and, if necessary, supplemented with other tests.
It can also help to assess heart rhythm abnormalities that occur during exercise, abnormal blood pressure responses, symptoms triggered by physical activity, exercise tolerance and recovery capacity. In people reporting fatigue, shortness of breath or a decline in performance, it can provide useful information to help decide whether further investigation is necessary.
The importance of measuring functional capacity has been demonstrated in large population-based studies. A meta-analysis published in JAMA analysed data from over 100,000 people and examined the relationship between cardiorespiratory fitness, mortality and cardiovascular events. The authors estimated that each increase of one metabolic equivalent (MET) – a measure of exercise capacity – was associated with an approximate 13 per cent reduction in the risk of all-cause mortality and a 15 per cent reduction in the risk of cardiovascular events.
Translated into clinical terms, findings such as these help to explain why functional capacity is no minor matter. It is not simply a question of ‘being fit’, but of assessing how the heart, lungs, circulatory system and muscles work together to sustain physical exertion.
Another important aspect is the blood pressure response during exercise. A systematic review and meta-analysis published in the *American Journal of Hypertension* found that a hypertensive response during moderate-intensity exercise was associated with an increased risk of cardiovascular events and mortality. This information should not be interpreted in isolation, but it does explain why blood pressure is monitored regularly during the test and why its behaviour during exercise can provide additional information to the cardiologist.
A test tailored to each patient
Another important point is that not all exercise tests are carried out in the same way. The protocol must be tailored to each person’s profile, including their age, physical condition, medical history and clinical objective.
Dr Hernández Hernández points out that “there are various protocols that can be adapted to the patient’s profile. Older people may be prescribed a gentler protocol, whilst higher-intensity protocols are used for younger people or athletes”.
This adaptation avoids two common mistakes: placing too much demand on those who need a more gradual assessment, or falling short for fit individuals who require sufficient intensity to obtain useful information.
For older people, patients with lower fitness levels or those with walking difficulties, the protocol may be more gradual. For young, active people or athletes, a higher-intensity test may be considered, always under medical supervision and in accordance with appropriate criteria. European guidelines on sports cardiology specifically emphasise that the assessment must be tailored to the type of exercise, the individual’s profile and their clinical context.
Conventional test and cardiopulmonary test with gas analysis
The conventional exercise test primarily records the electrocardiogram, heart rate, blood pressure and symptoms during exercise. In many patients, this information is sufficient to answer the clinical question at hand.
However, there are situations in which a more advanced assessment may be useful: the cardiopulmonary exercise test. In this test, the patient exercises whilst wearing a mask that allows respiratory gases to be analysed. This measures how much oxygen the body uses and how much carbon dioxide it expels during exercise.
This allows for a more comprehensive assessment of the functioning of the heart, lungs, circulation, muscles and metabolism. One of the best-known parameters is maximum VO₂ (oxygen consumption), which indicates the body’s maximum capacity to utilise oxygen during exercise. Other parameters can also be analysed, such as ventilatory efficiency or specific metabolic thresholds.
The guidelines published in the *European Heart Journal* on cardiopulmonary testing explain that this type of assessment can provide relevant information in specific clinical populations and help to better interpret the cause of exercise limitation when symptoms cannot be clearly explained by conventional tests.
Therefore, the choice between conventional exercise testing and a cardiopulmonary test does not depend on one being ‘better’ than the other in general terms, but rather on the specific question the cardiologist needs to answer for each patient.
What happens if the test suggests an abnormality
The exercise test is a functional test: it shows how the heart responds during exercise. If findings emerge that suggest a possible abnormality, it may be necessary to complete the investigation with anatomical or imaging tests.
Dr Hernández Hernández explains it as follows: “When the stress test suggests that there may be an abnormality, the usual course of action is to continue the investigation with another test—not a functional one, but an anatomical one—to assess the condition of the coronary arteries, which are the arteries that supply blood to the heart itself”.
These tests may include a coronary CT scan, a non-invasive technique that allows the coronary anatomy to be assessed, or cardiac catheterisation in selected cases, when a more direct assessment of the heart’s arteries is required.
This should not be interpreted in an alarmist manner. A finding on a stress test does not automatically equate to a serious condition. It means that the result must be analysed within the clinical context and that, in certain cases, it is advisable to obtain further information in order to make accurate decisions.
When it may be appropriate to have one
The decision to carry out a stress test must be made by a doctor. It can be useful in investigating symptoms that occur during physical activity, such as chest pain, shortness of breath, palpitations, dizziness, excessive tiredness or a decline in performance. It may also form part of a cardiological assessment for people with cardiovascular risk factors or for those who wish to start or resume physical activity more safely.
In active individuals or athletes, the test can help to assess the cardiovascular response to exercise, tailor recommendations and identify findings that require follow-up. European guidelines on sports cardiology emphasise that the assessment must be tailored to the type of exercise, the individual’s profile and their clinical context [6].
In the field of prevention, European guidelines on cardiovascular prevention highlight the importance of an individualised risk assessment, taking into account clinical factors, lifestyle habits, medical history and personal characteristics [8]. The exercise stress test does not replace this comprehensive assessment, but it can provide functional information when there is a specific medical concern.
How the patient should prepare
Preparation may vary depending on the type of test and the clinical situation, so the medical team’s instructions should always be followed. In general, it is advisable to wear comfortable clothing and suitable footwear for walking or cycling. It is also recommended to avoid heavy meals immediately before the test and to inform the medical team of any regular medication.
No treatment should be stopped on one’s own initiative. If any treatment regimen needs to be adjusted before the test, this must be indicated by the doctor.
It is also important to report any new symptoms that have arisen in the preceding days, such as chest pain, fever, a respiratory infection, dizziness, loss of consciousness, worsening shortness of breath or any other relevant clinical changes. If the patient has any cardiology reports, previous electrocardiograms, imaging scans or recent blood test results, it may be useful to provide these.
As Dr Hernández Hernández points out, this is a test that “can be undertaken by practically anyone who is in reasonably good physical condition and can walk about or walk well”.
A way of observing the heart in real-life situations
The stress test is valuable because it brings the cardiological assessment closer to a situation more akin to everyday life. Many people need to know not only how their heart is functioning at rest, but also how it responds when the body is active.
This information can help to investigate symptoms, guide diagnoses, assess functional capacity, determine whether further tests are needed, and support recommendations on physical activity, prevention and follow-up. The key lies in the medical interpretation. A normal test result can be reassuring, but it does not completely rule out cardiovascular risk. An abnormal result may require further investigation, but should not be interpreted in isolation or cause undue alarm. The true value becomes apparent when the data is integrated with the patient’s medical history, risk factors, symptoms and health goals.
At the Publio Cordón Memorial Hospital, the stress test is viewed as part of a cardiology approach focused not only on diagnosis, but also on prevention, personalised care and medical support. Because understanding how the heart responds when the body needs to perform does not mean looking for disease where there is none. It means gaining a better understanding of how the body functions when faced with the real demands of everyday life.
And, in many cases, that understanding can be the first step towards better looking after one’s cardiovascular health.
The information contained in this article is for informational purposes only and is not a substitute for a personalised medical assessment or individual recommendations for diagnostic tests.
The information in this article is provided for general awareness and does not replace an individualised medical assessment.
