VO2max and Telomeres: Why Fitness May Have a Threshold

You may not need elite endurance fitness to capture the telomere advantage linked with aerobic capacity. A 2025 meta-analysis found that people with a VO2max at or above the 70th age- and sex-adjusted percentile had longer telomeres than those below the 50th percentile, with a pooled standardized mean difference of 0.36. That is a small-to-moderate association, not a cellular fountain of youth. More surprising, people at or above the 90th percentile did not show an additional telomere advantage over the already-fit group.

The result gives a useful answer to a question biohackers tend to overcomplicate: if telomeres are the target, maximal VO2max may not be necessary. But the evidence does not show that training to a given percentile lengthens telomeres, reverses biological age, or adds years to life. Most of the relevant research is cross-sectional, meaning it compares people who already differ in fitness rather than randomly assigning them to become fitter.

The association: fitter people had longer telomeres

Ryall et al.'s 2025 systematic review and meta-analysis grouped participants using age- and sex-adjusted VO2max norms: fit meant at least the 70th percentile, unfit meant below the 50th percentile, and extremely fit meant at least the 90th percentile. Across the included cross-sectional evidence, the fit group had longer telomeres than the unfit group, with a pooled standardized mean difference of 0.36.

Standardized mean differences make studies using different laboratory methods easier to combine, but they are less intuitive than base pairs. Ryall and colleagues estimated that, if telomere-length variability in the population is roughly 600 to 1,000 base pairs, an SMD of 0.36 corresponds to about 216 to 360 base pairs. Using estimated age-related shortening rates of 20 to 40 base pairs per year, that works out to roughly 5 to 18 years of apparent biological-age difference.

That range should make readers cautious, not impressed by a large-looking number. It depends on assumptions about both telomere variation and the rate of shortening. Telomere length also differs substantially among people of the same chronological age. A blood test cannot tell you that you are exactly seven—or 17—years biologically younger because of your cycling habit.

The most practical finding was the apparent plateau. The meta-analysis found no incremental telomere benefit in the group at or above the 90th VO2max percentile compared with the group at or above the 70th percentile. This does not mean elite fitness lacks value for performance, cardiovascular risk, or other outcomes. It means this analysis did not find extra benefit for this one biomarker once participants had reached a moderately high fitness tier.

Why the result is plausible, but still not causal

Telomeres are repeating DNA sequences that cap chromosome ends. When cells divide, those caps can shorten; telomerase can add repeats back. That biology makes an exercise effect plausible. In a 2021 systematic review and meta-analysis by Denham et al., exercise training significantly increased expression of TERT, the gene encoding telomerase's catalytic subunit, and increased telomerase enzyme activity.

This is intervention evidence for an upstream pathway. It is not proof that exercise training preserves or lengthens telomeres in healthy adults over time. Enzyme activity and telomere length are different endpoints, and the body has a talent for making a plausible mechanism look more settled than the clinical evidence warrants.

A 2022 systematic review by Schellnegger et al. adds a useful interpretation: current fitness appeared more predictive of telomere length than cumulative exercise history. If that pattern holds, telomere biology may reflect a maintained physiological state rather than a permanent reward for the miles logged decades ago. Regular training matters more than an old race medal in a drawer.

Body composition muddies the picture

Fitness and leanness often travel together, and that creates a hard problem for observational research. A 2023 cross-sectional study by Shin et al. examined cardiorespiratory fitness, cardiovascular risk factors, and telomere length by age and obesity status. It supported an association between fitness and telomere length, while also identifying obesity as an important covariate. Lower BMI independently tracks with longer telomeres.

So the pooled VO2max association may reflect several connected factors: aerobic fitness itself, lower adiposity, diet, illness burden, smoking history, socioeconomic differences, or the fact that people with longer telomeres may simply be healthier enough to exercise more. Statistical adjustment can reduce some of that bias; it cannot fully erase it from a cross-sectional design.

Telomere measurement is a real limitation

Ryall et al. included studies using qPCR, terminal restriction fragment analysis, FISH, TESLA, and STELA. These methods do not report the same type of measurement or carry the same error profile. qPCR commonly produces a relative T/S ratio, while terminal restriction fragment methods can report base-pair length. Pooling them into a standardized effect is reasonable for synthesis, but it does not solve the underlying measurement differences.

The review also could not obtain individual participant data from 11 eligible studies. That missing information may bias the pooled estimate if unavailable studies differed systematically from those that could be reanalyzed. The excerpted report does not provide the heterogeneity statistics needed to judge the spread between studies precisely.

There is a second, more basic issue: most studies measure leukocyte telomere length. Blood-cell telomeres are a proxy, not a direct reading of telomere status in cardiac muscle, neurons, or other tissues relevant to aging. The link between leukocyte telomeres and tissue-specific telomere biology remains uncertain in exercise research.

A direct null result deserves attention

The literature does not speak with one voice. A 2023 study by Seki et al. found no strong association among physical fitness, telomere length, and DNA-methylation measures of biological aging. The study also found no strong association between physical fitness and the methylation markers it assessed.

This result does not cancel a meta-analysis, but it limits the confidence of any sweeping claim. Differences in population, fitness measures, telomere assays, sample characteristics, and statistical precision can produce different results. It also raises the possibility that the overall association is modest, population-specific, or sensitive to measurement noise. Claims that exercise reverses an epigenetic clock or that yoga has a special telomerase effect need separate, well-controlled evidence; this evidence does not establish either claim.

How to build aerobic fitness without treating HIIT as a religion

The telomere studies do not establish a superior training style. They point to cardiorespiratory fitness, not a particular playlist, interval format, or branded heart-rate zone. Both lower- and higher-intensity approaches can improve aerobic capacity.

A 2026 systematic review and meta-analysis by Nuuttila et al. found that low-intensity endurance training below the first lactate or ventilatory threshold improved aerobic fitness in working-age adults. This is the physiological territory often called zone 2, though the review used the more precise threshold-based definition rather than a universal percentage of VO2max.

For people who tolerate hard intervals, a 2023 systematic review and meta-analysis by Clifford et al. found that preoperative HIIT improved cardiorespiratory fitness in adults undergoing major surgery. That population differs from healthy community-dwelling adults, so it cannot prove that HIIT has a special telomere effect. It does support HIIT as one route to improving fitness.

Age does not close the door. A 2025 systematic review and meta-analysis of randomized trials in healthy adults aged 60 and older found that aerobic, resistance, and combined exercise training all improved VO2max or VO2peak. The telomere plateau itself has not been independently replicated across age groups, but aerobic fitness remains trainable later in life.

What to do with this evidence

• Aim for durable aerobic fitness. The 70th percentile is an interesting research threshold, but the underlying normative tables were not available here to convert it into a universal mL/kg/min target by age and sex.
• Use the training you can sustain. Low-intensity endurance work and HIIT can both raise aerobic fitness. Recovery capacity, injury risk, medical history, and adherence should choose the method.
• Keep body composition in view. Improving fitness and reducing excess adiposity may both matter, and current research cannot cleanly separate their telomere effects.
• Do not use telomere testing as a scorecard for your training block. Assay differences, tissue specificity, and normal biological variation make individual interpretation shaky.

The evidence supports aerobic fitness for its established health benefits. Longer leukocyte telomeres are a plausible bonus, not a proven payoff from crossing a VO2max threshold.

Ryall et al. note that each 1-MET increase in fitness has been associated with an 11% to 17% lower mortality risk. That outcome matters more than a modest cross-sectional difference in a blood-cell biomarker. Train toward a fitness level you can maintain, because the strongest reason to do it does not depend on telomeres behaving like a stopwatch.