The NASA Lean Test vs the Active Stand Test

The dispute over whether the NASA Lean Test belongs in clinical practice has less to do with physiology than with which test got written into a consensus statement first.

In January 2025, Clinical Autonomic Research published a letter titled Is the NASA Lean Test a suitable tool to diagnose cardiovascular autonomic disorders? The answer the authors give is no. They close by calling the NASA Lean Test, abbreviated NLT, "an improper shortcut to cardiovascular autonomic diagnoses." Several paragraphs earlier, in the same letter, they endorse a different bedside test in a single sentence: "Active standing tests can be used to screen for POTS."

That pairing is the part worth slowing down on. Two tests, neither requiring a tilt table. Both record heart rate and blood pressure across 10 minutes of upright posture. Both are performed in an ordinary exam room. One of them is a reasonable screen for POTS. The other is an improper shortcut. The entire weight of that distinction rests on what a patient's back is touching.

I do not think it can carry that weight. My position is that leaning and standing are the same category of test, that the NASA Lean Test is arguably the closer approximation of the tilt table rather than the further one, and that the dispute is a category error, because neither test was ever a diagnostic tool to begin with.

What the 2025 Clinical Autonomic Research letter says about the NASA Lean Test

The letter comes from Teuschl and 6 colleagues across Austrian, French, Croatian, Dutch and British autonomic centers. It is a serious document from serious people, and parts of it are correct.

Their case runs on 4 claims. First, no validation study has compared the diagnostic accuracy of the NLT against tilt table testing or active standing. In their words, "there are currently no structured data regarding the validity of a leaning test for the clinical autonomic diagnosis of orthostatic disorders." Second, the NASA experiments the test descends from studied small samples of healthy young men and astronauts, and were designed to characterize normal physiology under heat, exercise and bed rest, not to identify disorders. Third, NASA itself no longer uses lean tests and now runs a standard 10 minute active standing test. Fourth, during the COVID-19 pandemic patients began self-administering the NLT at home and diagnosing themselves with POTS, at high inaccuracy rates, using unreliable devices in uncontrolled settings.

The fourth point is simply true, and it deserves more agreement than it usually gets from people who like the lean test. A patient alone in a hallway with a consumer wrist monitor and no trained observer is not performing a clinical test at all. That failure has nothing to do with posture, though, and would apply just as completely to a self-administered active stand.

The crack in the argument shows up in the letter's own hedge about the leaning position. After acknowledging that the NLT protocol specifies only the shoulder blades contact the wall, with the heels 6 inches out, and that patients should avoid moving, tensing or shifting weight, the authors write that "it might be difficult to standardize body posture in a way to preclude the use of the calf muscle pump. A lean test may thus be interpreted as a mixture between active standing and passive tilt."

Read that sentence again with the conclusion in mind. A test described as a mixture of the 2 accepted methods is being placed outside the category that both of those methods define. If leaning genuinely sits on a continuum between active standing and passive tilt, then it lands as an intermediate point between 2 tests the same authors already accept.

Why leaning and standing are closer than the consensus admits

The consistent position is: tilt table is the reference standard because it removes the muscle pump entirely and standardizes recording. Standing and leaning are both convenient approximations with tradeoffs, and whichever one gets called 'acceptable' and which gets called 'an improper shortcut' seems to be a matter of who published first and got cited into consensus statements, not a clean physiological distinction.

The physiology here is not in dispute, and the letter states it plainly. Citing Plash and colleagues (2013), the authors note that "during active standing the skeletal muscle pump is active, which increases the venous return to the heart, in turn leading to a different cardiovascular response compared with passive tilt."

That is the whole variable. The skeletal muscle pump is what separates a tilt table from a stand test. Everything else about the 3 methods, the supine rest period, the 10 minute upright interval, the heart rate and blood pressure sampling, is broadly shared. So the only serious question about where the lean test belongs is a question of degree. How much muscle pump does leaning remove compared with standing unaided?

The letter's answer is that leaning cannot fully preclude the calf muscle pump. That is almost certainly right. But "cannot fully preclude" and "is no different from free standing" are very different claims, and only the first one is supported.

Notably, the field does not treat this as settled either. A research group in the Department of Neurology at the University of Utah has been running exactly this comparison, presented at the 2024 Undergraduate Research Symposium under the title Active Stand vs. NASA Lean: Searching for Agreement, with Melissa Cortez as research mentor. Their stated hypothesis is that variability in how patients lean against the wall may produce disagreement with the active stand. That is a poster, not a published trial, and it should be weighed as such. But the framing matters twice over. An open comparison study is not how a field treats a question it considers closed, and Cortez is a co-author of the 2021 NIH expert consensus on POTS. The people closest to the standards are still treating this as an empirical question.

Why I prefer the NASA Lean Test for orthostatic screening

My preference comes down to what free standing actually requires of a body.

Standing unaided is a continuous active task rather than a static posture. A person standing still sways, and correcting that sway recruits the calf and ankle musculature over and over for the entire 10 minutes. That is the same musculature that drives venous return. An active stand test therefore has the muscle pump switched on by design, and it stays on as long as the patient stays balanced.

A wall-braced lean removes the balance requirement. With the shoulder blades against the wall and the heels 6 to 8 inches forward, the wall absorbs the postural work that the calves would otherwise be doing. Pradeep Chopra, MD describes the position as one that "reduces the help your leg muscles normally give in pumping blood back to the heart, so it puts more stress on your circulation."

If the tilt table is the reference standard because it removes the muscle pump and standardizes posture, then the bedside test that removes more of the muscle pump is the better approximation of it. The NASA Lean Test is closer to a diet tilt table than to a diet active stand.

There is a second argument that has nothing to do with elegance and everything to do with who gets measured. The Bateman Horne Center notes that the active stand "can be challenging for very symptomatic patients to complete safely without support," while the lean is "safer for frail or highly symptomatic patients due to wall support and ease of assistance to the floor if needed." A test the sickest patients cannot finish produces missing data rather than cleaner data, selected against exactly the patients the test exists to find.

The strongest counterpoint to all of this is the letter's third claim, that NASA has moved on from lean tests to a 10 minute active stand. The letter does not say why, and I am not going to invent a reason. What I will say is that NASA evaluates astronauts readapting to gravity after spaceflight, a population and a question with almost nothing in common with screening a chronically ill patient who cannot stand unsupported for 10 minutes. An agency's internal protocol choice for its own operational population is weak evidence about diagnostic validity in a patient population.

The evidence base under the NASA Lean Test

The phrase "no structured data" is doing a great deal of work in this letter, and it deserves to be checked rather than repeated.

The letter itself cites the foundational comparison. Hyatt, Jacobson and Schneider (1975) compared 70 degree tilt, lower body negative pressure and passive standing before and after 2 weeks of bed rest. What is striking is that 2 careful parties read this same study in opposite directions. The Bateman Horne Center cites it as having "compared the passive stand test to TTT and found it to be as accurate." Teuschl and colleagues cite it to observe that heart rate changes were larger in the lean test than in the 70 degree tilt, in healthy subjects, in an experiment about normal physiology rather than disorder identification.

Both readings are defensible, which is the honest and slightly deflating point. The study enrolled 5 men. It cannot bear the weight either side puts on it. The evidence base beneath both bedside tests is simply thinner than the confidence gap between them implies.

What the lean test does have is a documented institutional trail. The passive stand was used in the CDC-sponsored Multi-site Clinical Assessment of ME/CFS study carried out from 2012 to 2017. The 10 minute passive stand was recommended for orthostatic intolerance assessment in the 2015 Institute of Medicine report on ME/CFS diagnostic criteria. Lee and colleagues (2020) published NLT hemodynamics showing circulatory decompensation in a subset of ME/CFS patients, and Vernon and colleagues (2022) used orthostatic challenge to separate symptomatic, hemodynamic and cognitive responses in long COVID and ME/CFS. Clinicians treating ME/CFS have used the passive stand since the 1990s.

None of that is a head-to-head diagnostic accuracy trial, and I am not going to pretend it is. That gap is real and the letter is right to name it. But the gap is in comparative validation, not in evidence of any kind, and it is the same gap the Utah group is currently trying to close.

Screening tests and diagnostic tests do different jobs

Here is where the whole argument comes apart, and it comes apart in a way that should end it.

Schools screen children for scoliosis with a forward bend test. A nurse looks at the curve of a spine for a few seconds. Nobody argues that this is a diagnostic failure because it is not a radiograph, and nobody writes letters calling it an improper shortcut to spinal diagnosis. Its job is to flag cases for someone else to confirm. A flagged child goes on to imaging, and the imaging decides.

The NASA Lean Test and the active stand are both the nurse. The tilt table is the imaging, and it earns that position precisely because it removes the muscle pump entirely and standardizes the recording conditions.

Every party to this dispute already agrees on that. The letter concludes that "the NLT may currently not be used as a diagnostic tool," which is a claim no serious proponent of the test contests. The Bateman Horne Center states that stand tests "cannot, by themselves, definitively diagnose the details of an autonomic disorder." The 2021 NIH consensus is explicit that hemodynamic thresholds alone do not make a POTS diagnosis, since the full clinical criteria include symptoms, duration and exclusion of other causes. A heart rate rise of 30 beats per minute is a finding. POTS is a diagnosis. Those are different objects.

So the sentence "the NLT may currently not be used as a diagnostic tool" is true, agreed upon by everyone, and completely beside the point, because nobody was using it as one. The actual argument is about which screen is acceptable. It has been dressed in the language of diagnosis, which makes it sound like a question about rigor when it is really a question about permission.

How citation priority decides which orthostatic test counts as legitimate

If the physiological gap between leaning and standing is a matter of degree, and both tests are screens rather than diagnostics, then something other than physiology is deciding which one is respectable.

Look at what each test carries behind it. The active stand has Finucane and colleagues (2019), a practical guide to active stand testing published in Clinical Autonomic Research. The tilt table has Thijs and colleagues (2021), a consensus statement of the European Federation of Autonomic Societies endorsed by the American Autonomic Society and the European Academy of Neurology. Both are cited in the letter. The NASA Lean Test has neither. What it has instead is 30 years of clinical use in ME/CFS practice, a patient population whose testing conventions grew up largely outside European autonomic neurology.

Then look at the authorship. Of the 7 authors on the 2025 letter, 5 are co-authors of the 2021 tilt table consensus statement it cites as the standard: Fanciulli, Pavy-Le Traon, Habek, Thijs and Struhal. That is not misconduct and I am not implying it is. Specialty fields are small, and the people who write consensus statements are the people who know the material. But the effect is worth naming plainly. The benchmark the NASA Lean Test is being measured against was written by most of the same people conducting the measurement, and the test that clears the benchmark is the one that was in the room when it was drafted.

That is the mechanism to watch. In POTS and ME/CFS research, whichever method reaches a consensus statement first becomes the default legitimate method, and everything arriving afterward has to argue its way back in against a standard it had no part in setting. That process rearranges the citation graph while leaving the underlying physiology exactly where it was.

The Bateman Horne Center, which has more reason than most to defend the lean test, does not defend it. Their stated position is that they "don't insist on one right stand test," and that what matters is that more people with symptoms get recognized, validated, diagnosed and treated. That is the correct posture toward 2 screening tools separated by a wall. Run whichever one the patient in front of you can safely complete, take the numbers seriously, apply the full clinical criteria before naming a diagnosis, and refer to tilt when the picture is unclear or conservative care fails.

The patients arguing about this on the internet are not the ones who invented the confusion. They inherited a field where the reference standard is scarce, the screens are contested, and the contest is being settled by publication order.

Sources

1. Teuschl Y, Fanciulli A, Pavy-Le Traon A, Habek M, Thijs RD, Pavelic AR, Struhal W (2025). Is the NASA Lean Test a suitable tool to diagnose cardiovascular autonomic disorders? Clinical Autonomic Research 35(3):529-531. doi:10.1007/s10286-024-01097-2. https://pmc.ncbi.nlm.nih.gov/articles/PMC12137516/
2. Plash WB, Diedrich A, Biaggioni I, Garland EM, Paranjape SY, Black BK, Dupont WD, Raj SR (2013). Diagnosing postural tachycardia syndrome, comparison of tilt testing compared with standing haemodynamics. Clinical Science 124:109-114. https://pmc.ncbi.nlm.nih.gov/articles/PMC3478101/
3. Hyatt KH, Jacobson LB, Schneider VS (1975). Comparison of 70 degrees tilt, LBNP, and passive standing as measures of orthostatic tolerance. Aviation, Space, and Environmental Medicine 46:801-808. https://pubmed.ncbi.nlm.nih.gov/1156287/
4. Bateman L (2026). Orthostatic Intolerance Testing Made Clear, Tilt Table, Active Stand, and the Passive Stand. Bateman Horne Center. https://batemanhornecenter.org/orthostatic_intolerance_testing_made_clear/
5. Lameman C, mentor Cortez M (2024). Active Stand vs. NASA Lean, Searching for Agreement. University of Utah Undergraduate Research Symposium, Department of Neurology. https://our.utah.edu/urs/active-stand-vs-nasa-lean-searching-for-agreement/
6. Vernino S, Bourne KM, Stiles LE, et al. (2021). Postural orthostatic tachycardia syndrome (POTS), State of the science and clinical care from a 2019 National Institutes of Health Expert Consensus Meeting, Part 1. Autonomic Neuroscience 235:102828. https://pmc.ncbi.nlm.nih.gov/articles/PMC8455420/
7. Lee J, Vernon SD, Jeys P, Ali W, Campos A, Unutmaz D, Yellman B, Bateman L (2020). Hemodynamics during the 10-minute NASA lean test, evidence of circulatory decompensation in a subset of ME/CFS patients. Journal of Translational Medicine 18:314. https://pmc.ncbi.nlm.nih.gov/articles/PMC7429890/
8. Vernon SD, Funk S, Bateman L, et al. (2022). Orthostatic challenge causes distinctive symptomatic, hemodynamic and cognitive responses in long COVID and myalgic encephalomyelitis/chronic fatigue syndrome. Frontiers in Medicine 9:917019. https://pmc.ncbi.nlm.nih.gov/articles/PMC9285104/
9. Unger ER, Lin JS, Tian H, Natelson BH, Lange G, Vu D, Blate M, Klimas NG, Balbin EG, Bateman L, et al. (2017). Multi-Site Clinical Assessment of Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (MCAM), Design and Implementation of a Prospective/Retrospective Rolling Cohort Study. American Journal of Epidemiology 185(8):617-626. https://pmc.ncbi.nlm.nih.gov/articles/PMC5565838/
10. Finucane C, van Wijnen VK, Fan CW, et al. (2019). A practical guide to active stand testing and analysis using continuous beat-to-beat non-invasive blood pressure monitoring. Clinical Autonomic Research 29:427-441. https://pubmed.ncbi.nlm.nih.gov/31076939/
11. Thijs RD, Brignole M, Falup-Pecurariu C, et al. (2021). Recommendations for tilt table testing and other provocative cardiovascular autonomic tests in conditions that may cause transient loss of consciousness. Autonomic Neuroscience 233:102792. https://pubmed.ncbi.nlm.nih.gov/33752997/
12. Chopra P (2025). Standing Tests for POTS, Active Stand, NASA Lean. https://www.painri.com/post/standing-tests-for-pots-active-stand-nasa-lean