An exercise stress test, often called a treadmill test, evaluates how the heart and circulatory system respond to physical exertion. The test measures your maximum functional capacity, which is the highest level of physical work you can achieve. This capacity is quantified using the Metabolic Equivalent of Task (MET), a powerful indicator of overall cardiovascular health. Understanding your MET score provides insight into your current fitness level and potential long-term health outlook.
What is a Metabolic Equivalent of Task (MET)?
The Metabolic Equivalent of Task (MET) is a standardized physiological measure expressing the energy cost of physical activities. One MET is defined as the approximate amount of oxygen consumed by a person at rest (3.5 mL O2/kg/min). This resting rate serves as the baseline for all subsequent measurements during the stress test.
When performing an activity, the MET score indicates how many times greater the energy expenditure is compared to being at rest. For instance, an activity rated at 4 METs requires four times the oxygen consumption of sitting still. During a stress test, the final MET score achieved represents your peak oxygen uptake and maximum functional capacity—the highest physical workload your body could sustain.
To illustrate, walking slowly on a flat surface might be a 2 MET activity, while brisk walking is around 4 METs. More vigorous activities, such as running, are typically 8 METs or higher, demonstrating the exponential increase in energy demand. The score reported from your stress test is the maximum MET level reached, providing a single, objective number for your cardiorespiratory fitness.
Interpreting Your Stress Test Score
The MET score is a strong predictor of future cardiovascular events and all-cause mortality, often considered more significant than other test results. A higher score correlates directly with a lower risk of serious health issues over the long term. Generally, scores are categorized into ranges to help assess risk and prognosis.
A score of less than 5 METs is classified as poor functional capacity, associated with a significantly increased risk of adverse cardiovascular outcomes. Individuals in this range may struggle with simple daily activities like climbing two flights of stairs. Achieving between 5 and 8 METs is considered fair or moderate capacity, suggesting a need for lifestyle improvements to enhance cardiorespiratory fitness.
Scores between 9 and 11 METs are generally viewed as good, representing a functional capacity that offers a favorable prognosis. An excellent score is 12 METs or more, which is strongly associated with an excellent long-term outlook, even in patients with known coronary artery disease. Achieving 10 METs or more is a benchmark for a low-risk profile in healthy adults. Research shows that every 1-MET increase in exercise capacity is linked to a significant reduction in the risk of all-cause mortality and coronary events.
Variables That Affect MET Score Results
While the MET score is an objective measure of functional capacity, several non-cardiac variables can influence the final result. Age is a primary factor, as maximal functional capacity naturally declines over the lifespan. A score excellent for a 70-year-old may be considered average for a 40-year-old, meaning results must be interpreted relative to age and sex.
Baseline fitness level plays a considerable role, with sedentary individuals achieving lower scores than those who engage in regular aerobic exercise. Patients with limited physical conditioning may end the test early due to muscle fatigue rather than true cardiac limitation, leading to an underestimation of their actual heart health. This result is termed an endpoint-limited test, as opposed to a symptom-limited test, which stops due to symptoms like chest pain or shortness of breath.
Medications can also suppress the measured MET score, particularly beta-blockers, which are commonly prescribed for heart conditions and high blood pressure. These drugs intentionally lower the maximum heart rate, preventing the patient from reaching their full predicted workload. Patients on beta-blockers may achieve a lower MET score, making it necessary to use alternative percentage thresholds for risk assessment.
Strategies for Improving Functional Capacity
Improving your MET score enhances your overall cardiorespiratory fitness and long-term prognosis. The most effective strategy involves consistent aerobic exercise, aiming for activities that elevate your heart rate and challenge your current capacity. This conditioning improves the efficiency of your heart and lungs in delivering oxygen to your working muscles.
Establishing a regular routine that incorporates both the frequency and duration of exercise is far more beneficial than sporadic, intense workouts. For individuals aiming to raise a low score, a structured cardiac rehabilitation program can be highly effective, often leading to a clinically significant increase in MET levels.
Complementary lifestyle modifications, such as maintaining a healthy weight, are also important for improving functional capacity. Weight management reduces the workload on the heart, making it easier to sustain higher levels of physical activity. Always consult with a physician or qualified healthcare professional before beginning any new rigorous exercise regimen to ensure it is appropriate for your specific health status.