Cardiopulmonary Exercise Testing Explained...for Regular People
Part 1: CPET Procedure
In a previous post, I described how cardiopulmonary exercise testing (CPET) has changed the game in myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) research and clinical practice. CPET has provided a wealth of objective physiological evidence supporting what patients have always told us. When done two days in a row, CPET can be used to assess the failure to recover after exertion, which appears central to ME/CFS pathophysiology.1
CPET is often discussed in the patient, scientific, and clinical communities. However, I find it that even very informed people may not know very much about the test itself, how the data is collected, and what the data means. Even my own phone autocorrects my speech-to-text dictations of “CPET” to “Sea Pet” and “CPAP.” It must think I own a massive marine aquarium where…I do sleep studies?
The next couple of posts will describe CPET. This first one will discuss the procedure. The next one will describe the data, how we analyze it, and how we interpret it.
Hopefully you will find both posts to be understandable even if you are not involved in research and clinical practice. And if you are, I hope these posts are an accessible reminder and primer to share with your patients.
What’s a “CPET?”
CPET test is a supervised physical stress test.2 We use it to evaluate how the body responds to physical exertion as demands increase.2 In healthy people and most clinical populations (even very ill ones), CPET results are highly reproducible from one day to the next. ME/CFS stands apart because reproducibility often breaks down after exertion.3-9 This is finding is often held up as an objective marker of PEM.5 More on that in a future post.
How a CPET Looks
The type of CPET set-up we use involves pedaling a stationary bicycle.1 We use a stationary bike rather than a treadmill to improve safety, and to precisely control and measure workload. This allows us to avoid the risk for falling, stop the test quickly if needed, and to pick important timepoints during the test during later analysis. The stationary bicycle has an automatic brake. This allows us to apply a known amount of resistance to the pedals throughout the test, making it progressively harder. The person just needs to maintain a constant rate of pedaling throughout the test.
We start by placing a lightweight mask over the person’s nose and mouth. The mask is connected to a plastic tube going into a machine that analyzes the gas composition of each breath. The computer uses a sensor to measure how much oxygen is consumed, breath by breath, from exhaled air. We know the content of oxygen in room air and we measure the gases expired each breath for oxygen and carbon dioxide. The balance of oxygen and carbon dioxide that we measure during CPET reflects what we call “gas exchange.”
We also keep track of heart rate, blood pressure, and how hard the person is pushing against the pedals continuously throughout the test. This setup allows us to see how efficiently the body is producing energy, how those systems change as the test becomes more challenging, and how much work all these changes are resulting in.
Typically, each CPET session would begin with unloaded cycling.2 This means the person pedals at zero resistance for three minutes while we gather some baseline data. Resistance then increases gradually in a continuous fashion until the individual reaches their limit, typically within eight to twelve minutes. Continuous application of resistance is called a ramping protocol.
However, we do not start our CPETs with three minutes of unloaded cycling.1 We found even unloaded cycling was too taxing on the patient. People were going through the test and hitting their maximal exertion too quickly to gather enough data to be able to comment on the physiology of what happened. Instead, we have modified the protocol to have a person do a 3-minute seated rest period on the bike before the ramping protocol starts.
We call the test a maximal CPET because, if the person is able, we are trying to achieve a certain set of accepted objective criteria that ensure accurate interpretation.1 Unlike a lot of so-called submaximal tests that involve a lower amount of physical exertion for a longer period of time, people work only briefly at a maximal level.
If the person needs to stop the CPET at any time and for any reason, we stop immediately. The patient remains in control at all times.
Recovering After CPET
For many patients, the most difficult part of the two-day CPET begins after leaving the laboratory. Symptoms often worsen within hours of the first test and intensify after the second.10,11 Part of the testing is to follow up with questionnaires to see how the recovery process unfolds. Research consistently documents post-test increases in fatigue, cognitive dysfunction, pain, and autonomic symptoms in people with ME/CFS that we do not see in sedentary people.10-13
Planning ahead for recovery is essential for CPET.1 We advise patients to rest aggressively, pace activities carefully, and minimize physical and cognitive strain after testing. We do not allow people to drive themselves to and from CPET appointments. For people traveling to see us from out of town, we always recommend a period of rest after the CPET before their return trip.
We recommend hydration, electrolyte support, and environmental modifications to promote recovery.1 We are studying different “PEM busting” types of treatments, as well, to reduce symptoms and improve recovery times. More on this in a future post.
Recovery takes as long as it takes. The time it takes to recover after a two-day CPET varies widely. The good news is long-term effects appear to be very rare.14 Some people return to their self-reported baseline within a few days, while others require two weeks or longer.13,14 This uncertainty is one of the most important considerations when deciding whether to undergo CPET.
We don’t yet know why some people recovery quickly and some people recover slowly. However, we do know that it doesn’t seem to be a simple matter of severity. We are in the process of looking into the physiological predictors of recovery duration. Hopefully this will improve our ability to predict how long it will take for people to recover after CPET. Stay tuned.
Deciding Whether to Do a CPET
From a patient perspective, the key question is not whether the test can be completed, but whether the information gained justifies the payback associated with PEM. Two-day CPET may be appropriate when objective documentation is needed to confirm a diagnosis,2,15 to establish objective evidence of disability,16 or for research purposes.15,17 Not everyone will benefit from a CPET.15 It is usually inappropriate for individuals with severe illness or limited recovery capacity.15
Just because CPET is not for everyone also doesn’t mean it’s for no one. The decision to go forward with CPET always should rest with the individual, balancing one’s own risks and benefits with input from trusted and knowledgeable others. Choosing not to undergo testing is always valid.
Conclusion
For decades, people with ME/CFS were told their symptoms could not be measured. CPET is an accessible way to objectively validate the physiological basis for signs and symptoms.
Next up: what does all the data mean?
References
1. Stevens S, Snell C, Stevens J, Keller B, VanNess JM. Cardiopulmonary Exercise Test Methodology for Assessing Exertion Intolerance in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome. Front Pediatr. 2018;6:242. doi:10.3389/fped.2018.00242
2. Balady GJ, Arena R, Sietsema K, et al. Clinician’s Guide to cardiopulmonary exercise testing in adults: a scientific statement from the American Heart Association. Circulation. Jul 13 2010;122(2):191-225. doi:10.1161/CIR.0b013e3181e52e69
3. Davenport TE, Stevens SR, Stevens J, Snell CR, Van Ness JM. Properties of measurements obtained during cardiopulmonary exercise testing in individuals with Myalgic Encephalomyelitis/Chronic Fatigue Syndrome. Work. 2020;66(2):247-256. doi:10.3233/WOR-203170
4. Franklin JD, Graham M. Repeated maximal exercise tests of peak oxygen consumption in people with myalgic encephalomyelitis/chronic fatigue syndrome: a systematic review and meta-analysis. Fatigue: Biomedicine, Health & Behavior. 2022;10(3):119-135.
5. Lim EJ, Kang EB, Jang ES, Son CG. The prospects of the two-day cardiopulmonary exercise test (CPET) in ME/CFS patients: a meta-analysis. J Clin Med. Dec 14 2020;9(12)doi:10.3390/jcm9124040
6. 1. Keller B, Receno CN, Franconi CJ, et al. Cardiopulmonary and metabolic responses during a 2-day CPET in myalgic encephalomyelitis/chronic fatigue syndrome: translating reduced oxygen consumption to impairment status to treatment considerations. J Transl Med. Jul 5 2024;22(1):627. doi:10.1186/s12967-024-05410-5
7. van Campen C, Visser FC. Female patients with myalgic encephalomyelitis/chronic fatigue syndrome or idiopathic chronic fatigue: comparison of responses to a two-day cardiopulmonary exercise testing protocol. Healthcare (Basel). Jun 5 2021;9(6)doi:10.3390/healthcare9060682
8. van Campen CLM, Rowe PC, Visser FC. Two-day cardiopulmonary exercise testing in females with a severe grade of myalgic encephalomyelitis/chronic fatigue syndrome: comparison with patients with mild and moderate disease. Healthcare (Basel). Jun 30 2020;8(3)doi:10.3390/healthcare8030192
9. van Campen CLMC, Rowe PC, Visser FC. Validity of 2-day cardiopulmonary exercise testing in male patients with myalgic encephalomyelitis/chronic fatigue syndrome. Advances in Physical Education. 2020;10(1)doi:10.4236/ape.2020.101007
10. Mateo LJ, Chu L, Stevens S, et al. Post-exertional symptoms distinguish myalgic encephalomyelitis/chronic fatigue syndrome subjects from healthy controls. Work. 2020;66(2):265-275. doi:10.3233/WOR-203168
11. Van Ness JM, Stevens SR, Bateman L, Stiles TL, Snell CR. Postexertional malaise in women with chronic fatigue syndrome. J Womens Health (Larchmt). Feb 2010;19(2):239-44. doi:10.1089/jwh.2009.1507
12. Davenport TE, Chu L, Stevens SR, Stevens J, Snell CR, Van Ness JM. Two symptoms can accurately identify post-exertional malaise in myalgic encephalomyelitis/chronic fatigue syndrome. Work. Mar 13 2023;doi:10.3233/WOR-220554
13. Davenport TE, Stevens SR, Baroni K, Van Ness M, Snell CR. Diagnostic accuracy of symptoms characterising chronic fatigue syndrome. Disabil Rehabil. 2011;33(19-20):1768-75. doi:10.3109/09638288.2010.546936
14. Moore GE, Keller BA, Stevens J, et al. Recovery from exercise in persons with myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS). Medicina (Kaunas). Mar 15 2023;59(3)doi:10.3390/medicina59030571
15. Davenport TE, Stevens SR, Van Ness M. Myalgic Encephalomyelitis. In: Ozemek C, American College of Sports Medicine, eds. ACSM’s Guidelines for Exercise Testing and Prescription. 11th ed. Lippincott Williams & Wilkins; 2025.
16. Ciccolella ME, Davenport TE. Disability law and the simplification of science: scientific and legal challenges to the functional capacity evaluation in individuals with chronic fatigue syndrome. Fatigue: Biomedicine, Health & Behavior. 2013;1(4):243-255. doi:10.1080/21641846.2013.828960
17. United States National Academy of Medicine. Beyond Myalgic Encephalomyelitis/Chronic Fatigue Syndrome: Redefining an Illness. NAM; 2015 Feb 10. The National Academies Collection: Reports funded by National Institutes of Health. Available from: https://www.ncbi.nlm.nih.gov/books/NBK274235/ doi: 10.17226/19012