From the Guidelines
For an average adult, achieving a METS level of at least 7-10 is generally recommended as the target during a treadmill stress test. This target represents moderate to high exercise intensity and is considered adequate for evaluating cardiovascular function. The specific target may vary based on age, gender, and fitness level, with younger adults typically expected to achieve higher METS (10+) and older adults possibly having lower targets (7+) 1. During the test, the treadmill speed and incline gradually increase to elevate the heart rate to at least 85% of the age-predicted maximum (calculated as 220 minus age). Reaching this target is important because it allows cardiologists to properly assess cardiac function under stress and detect potential coronary artery disease.
- Key points to consider:
- Failure to achieve the target METS level may result in an inconclusive test that doesn't adequately stress the heart to reveal underlying issues.
- The test should be stopped if the patient experiences chest pain, significant arrhythmias, concerning blood pressure changes, or severe fatigue before reaching the target METS level.
- Standard treadmill protocols initiate exercise at 3.2 to 4.7 metabolic equivalents (METs) of work and increase by several METs every 2 to 3 minutes of exercise (e.g., modified or standard Bruce protocol) 1.
- Gentler treadmill protocols, with incremental stages of 1 MET, or bicycle stress can help some patients achieve maximal exercise capacity.
- Optimal candidates with sufficient physical functioning may be identified as those capable of performing at least moderate physical functioning (i.e., performing at least moderate household, yard, or recreational work and most activities of daily living) and with no disabling comorbidity (including frailty, advanced age, marked obesity, PAD, chronic obstructive pulmonary disease, or orthopedic limitations) 1.
- Considerations for specific patient populations:
- Patients incapable of at least moderate physical functioning or with disabling comorbidity should be referred for pharmacological stress imaging.
- In the setting of submaximal exercise and a negative stress ECG, consideration should be given to performing additional testing with pharmacological stress imaging to evaluate for inducible ischemia 1.
- For patients with poor (<4 METs) or unknown functional capacity, pharmacological stress testing is appropriate, and exercise stress testing may be reasonable to perform if the patient's functional capacity is unknown 1.
From the Research
METS Levels for Treadmill Stress Test
To reach the target on a treadmill stress test, the recommended METS (Metabolic Equivalent of Task) level can vary depending on the individual's fitness level and the specific goals of the test.
- A study published in 1987 2 found that panic attack patients had a significantly higher heart rate at 4 and 6 METS than control groups, with a maximum METS level of 11.2 +/- 2.3.
- Another study from 2014 3 evaluated the prognostic value of treadmill stress echocardiography at extremes of exercise performance, including submaximal (<85% maximum predicted heart rate) versus high exercise capacity (≥ 10 metabolic equivalents, METS).
- The 2014 study 3 found that achieving a high exercise capacity of ≥ 10 METS was a predictor of favorable prognosis, with an overall low cardiac event rate of 0.4%/year.
Target METS Levels for Average Adults
For an average adult, the target METS level on a treadmill stress test may be around 7-10 METS, depending on the individual's fitness level and the specific goals of the test.
- However, it's essential to note that the target METS level can vary depending on the individual's health status, fitness level, and the specific protocol being used.
- A study from 1998 4 described a submaximal treadmill procedure for establishing individualized target Ratings of Perceived Exertion, which may be useful for developing target METS levels for outpatient cardiac rehabilitation patients.
Factors Influencing Target METS Levels
Several factors can influence the target METS level on a treadmill stress test, including:
- Fitness level: Fitter individuals may be able to achieve higher METS levels than less fit individuals.
- Health status: Individuals with certain medical conditions, such as heart disease, may need to aim for lower METS levels.
- Age: Older adults may need to aim for lower METS levels due to decreased physical fitness and increased risk of cardiovascular disease.
- The specific goals of the test: The target METS level may vary depending on the specific goals of the test, such as diagnosing cardiovascular disease or assessing fitness level.