Can running 100 marathons actually slow down how fast you age?

What happens to your fitness if you keep training for decades? A study published this year offers a fascinating clue. Researchers examined 340 people who had each completed at least 100 marathons and found that, even into older age, their aerobic fitness remained remarkably high compared with their peers.

What the data showed

Researchers Lundy, Reilly and Fleming (2026), publishing in Scientific Reports, surveyed 340 multi-marathoners with an average age of 52, from 24 countries. Their VO₂max estimates came from their own wearable devices, including Garmin, Polar and COROS. VO₂max is a measure of cardiorespiratory fitness: how effectively your body can take in, transport and use oxygen during intense exercise. The researchers compared these estimates with a large US reference database, accounting for age and sex.

The pattern was striking. Across every age group, the marathoners' estimated VO₂max sat well above population norms, with several groups above the 95th percentile for their age. More interesting than the raw numbers was the age-related pattern. Older participants remained exceptionally fit relative to their peers, and the cross-sectional decline in VO₂max across age groups appeared shallower than expected from population data. Older women in the cohort showed an especially large relative advantage compared with age-matched norms.

There is an important caveat. This was a cross-sectional survey of a highly self-selected group of committed endurance athletes, not a study that followed the same people as they aged. VO₂max was also taken from consumer wearables rather than measured directly in a laboratory.

It therefore cannot tell us whether decades of marathon running preserved their VO₂max, or whether people genetically and physiologically equipped to retain high fitness were more likely to become multi-marathoners in the first place. These athletes may also differ from the wider population in other ways, including health behaviours and underlying physiology.

What the study gives us is a fascinating snapshot of what exceptionally high cardiorespiratory fitness can look like in people who remain highly active into later life. It does not prove that running 100 marathons slows ageing.

Why cardiorespiratory fitness matters

This matters even if you have absolutely no intention of running a marathon.

Cardiorespiratory fitness is one of the strongest measurable predictors of long-term mortality risk. A landmark study of more than 122,000 adults undergoing treadmill testing, followed for a median of 8.4 years, found a strong relationship between higher fitness and lower all-cause mortality (Mandsager et al., 2018).

People in the lowest fitness category had roughly five times the mortality risk of those in the elite fitness category. Even people classified as elite had lower mortality than those in the high-fitness group, with no upper limit of benefit observed within this cohort.

Importantly, the relationship was also seen in older adults and people with hypertension.

This does not mean everyone needs elite-level fitness. In fact, one of the most practically useful findings was at the other end of the curve: moving out of the lowest fitness category was associated with a substantial reduction in mortality risk.

What this means if you are not about to run 100 marathons

You do not need to become an ultra-endurance athlete to benefit.

The World Health Organisation recommends that adults accumulate 150 to 300 minutes of moderate-intensity aerobic activity, or 75 to 150 minutes of vigorous activity, each week, alongside muscle-strengthening activity on two or more days (Bull et al., 2020).

And you do not have to hit those numbers perfectly before exercise starts to count. Health benefits can occur below the recommended range too, particularly for people moving from very low levels of activity.

What the marathoners illustrate is something slightly different. They show us just how high cardiorespiratory fitness can remain in people who continue to be exceptionally active into later life. Whether decades of endurance training directly caused their flatter age-related pattern requires longitudinal research.

There may be psychological advantages to maintaining an active lifestyle too. Training towards a goal can provide structure, mastery and motivation, while clubs, classes and training groups can add a social dimension that makes exercise easier to sustain.

The lesson is not to run 100 marathons. It is to stop treating cardiorespiratory fitness as something that only matters when you are young, athletic or training for an event.

Have a go...

1. Track consistency, not intensity spikes. Build regular aerobic activity into your week rather than relying on occasional heroic sessions. Fitness is something you maintain, not something you complete.
2. Aim for the WHO recommendations as a useful target. Work towards at least 150 minutes of moderate-intensity activity, or 75 minutes of vigorous activity, each week. If you are currently doing much less, start there. Some activity is better than none.
3. Add two strength sessions a week. WHO guidelines recommend muscle-strengthening activity involving the major muscle groups on two or more days each week alongside aerobic exercise.
4. Give yourself something to train towards. It does not have to be a marathon. A 5K, cycling event, hiking trip or simply improving your walking pace can give your training direction and make progress tangible.
5. Do not chase "elite" if you are starting from low fitness. The Mandsager data suggest that some of the most meaningful differences in mortality risk are seen when moving away from very low cardiorespiratory fitness. You do not need to be exceptional for improving your fitness to matter.

The lesson is not that we should all start training for marathons. It is that fitness is worth protecting as we age. Cardiorespiratory fitness tells us far more than how fast or how far we can go. It is closely linked to long-term health and survival, and the good news is that you do not need to be an endurance athlete to improve it. The goal is not 100 marathons. It is to keep moving, keep challenging your cardiovascular system, and keep building the fitness you want to carry into later life.

References:

Bull, F. C., Al-Ansari, S. S., Biddle, S., Borodulin, K., Buman, M. P., Cardon, G., Carty, C., Chaput, J.-P., Chastin, S., Chou, R., Dempsey, P. C., DiPietro, L., Ekelund, U., Firth, J., Friedenreich, C. M., Garcia, L., Gichu, M., Jago, R., Katzmarzyk, P. T., ... Willumsen, J. F. (2020). World Health Organization 2020 guidelines on physical activity and sedentary behaviour. British Journal of Sports Medicine, 54(24), 1451–1462. 

Lundy, L., Reilly, R. B., & Fleming, N. (2026). VO₂max ageing and all cause mortality in a global cohort of multi marathoners. Scientific Reports, 16, 21761. 

Mandsager, K., Harb, S., Cremer, P., Phelan, D., Nissen, S. E., & Jaber, W. A. (2018). Association of cardiorespiratory fitness with long-term mortality among adults undergoing exercise treadmill testing. JAMA Network Open, 1(6), e183605.