Your VO₂max Barely Changed After Training, Does That Mean You’re a Poor Responder?

You finish a training program, repeat your VO₂max test, and the number has barely moved. It is easy to turn that result into a description of yourself: perhaps your body simply does not respond well to aerobic training. A single change score carries less certainty than that label suggests.

The HERITAGE Family Study illustrates why the question is tempting. Participants completed a standardized 20-week aerobic training program, yet their measured changes in VO₂max varied widely. Some improved substantially, some changed little, and a small number recorded slightly lower values after training. Those results document variation in observed test changes, but they do not by themselves establish equally large differences in each person’s underlying capacity to adapt.¹

A before-and-after change contains more than the biological effect of training. Measurement error and ordinary within-person variation can influence both tests, so subtracting one value from the other does not isolate “trainability.” Reviews of exercise-response research have therefore cautioned against classifying people as responders or non-responders without accounting for these additional sources of variation.^2,3

A 2024 systematic review and meta-analysis addressed this problem by using non-exercising comparison groups to estimate variability that could occur without the training intervention. Much of the variation seen in VO₂max change scores was consistent with measurement error and other background variation captured by those groups. After accounting for that variability, the analysis found no strong evidence that the exercise interventions produced meaningful between-person differences in VO₂max trainability beyond it.²

That does not mean everyone must adapt identically. It means that a single observed change is a noisy way to estimate how differently two people truly responded to training. The same person may also be classified differently depending on the outcome measured, the threshold used to define a response, and the uncertainty around the measurement.^2,3

HERITAGE also found that observed VO₂max responses clustered within families and estimated a substantial familial and genetic contribution to the response pattern. That finding supports a role for inherited influences, but a heritability estimate is not a forecast of how one particular person will respond to a future program. Interpreting those older response data also requires the same caution about measurement and within-person variability emphasized in more recent methodological work.^1,3,4

Genetics has not yet solved the prediction problem. A systematic review identified many genes and variants associated with VO₂max trainability, but relatively few findings had been reproduced by more than two independent research groups. Differences in study populations, training programs, sample sizes, and other environmental influences further limited the ability to predict an individual response confidently.⁵

When a measured improvement is small, its size is best interpreted alongside the reliability of the test, day-to-day variation, and the training dose that was actually completed. One pre-to-post result can describe what was measured after one program; it cannot, on its own, establish a fixed personal ceiling for future adaptation.^2,3

A small number on a test report may be worth looking at more closely. It does not have to become a permanent label about what your body is capable of doing.