How Heat Affects Runners Differently By Age: NYC Marathon Data Reveals the Pattern

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You already know that running in the heat is harder. But you might assume that heat slows everyone down by roughly the same amount. It doesn't. A 2022 study published in Frontiers in Physiology analyzed pacing data from the New York City Marathon and found that the size of the heat penalty depends heavily on your age and sex.

If you're a runner over 30, this matters. The data shows that what feels like a "warm but manageable" race day for a 25-year-old can be a serious performance threat for a 45-year-old running the same pace.

What Did the NYC Marathon Study Actually Find?

The researchers looked at marathon finishing data across multiple age groups, tracking how running speed changed as race-day temperatures increased. They measured not just overall finish times but pacing patterns, specifically whether runners held an even pace or slowed down in the second half (positive splitting).

The core finding: heat hurts older runners more. Runners in their 20s showed the smallest speed losses as temperatures rose. The effect got bigger with each decade of age, peaking for men in their 30s through 60s and women in their 40s through 60s.

This wasn't a subtle difference. The gap between how a 25-year-old and a 55-year-old responded to the same temperature increase was large enough to change race outcomes.

Why Does Heat Hit Older Runners Harder?

Your body cools itself during running through two main systems: sweating and redirecting blood flow to the skin. Both of these systems decline with age.

A 2021 review in the Journal of Science and Medicine in Sport examined the thermoregulatory changes that happen as athletes age. The findings paint a clear picture:

• Sweat output per gland drops. Older adults have roughly the same number of sweat glands as younger adults, but each gland produces less sweat. The total cooling capacity goes down.
• Cardiac output is lower. Your heart has to do two jobs during hot running: deliver blood to working muscles and send blood to the skin for cooling. With age, the total cardiac output available for both tasks decreases.
• Vasodilation slows down. The blood vessels near the skin surface are slower to open up in older adults. This delays heat transfer from the core to the skin.
• Thirst sensation weakens. Older adults are more likely to under-hydrate because the thirst signal becomes less reliable with age.

The result is a compounding problem. An older runner generates the same amount of heat per unit of effort but has fewer tools to get rid of it. The core temperature rises faster, and the body's response to that rise is slower.

Does Fitness Level Change the Picture?

Here's some encouraging news. Research from the Gatorade Sports Science Institute and others shows that high aerobic fitness significantly improves thermoregulation at any age. Well-trained masters runners show better sweating responses, higher cardiac output, and more efficient skin blood flow than sedentary people of the same age.

But "better than sedentary" is not the same as "equal to younger runners." Even well-trained older athletes still show measurable declines in heat dissipation compared to well-trained younger athletes at the same relative intensity. Fitness narrows the gap. It doesn't close it.

This is why the NYC Marathon data is so valuable. These aren't sedentary people. They're marathon finishers. And even among this self-selected group of trained runners, the age-based heat penalty was clear and consistent.

How Does Heat Change Your Pacing Strategy?

The NYC Marathon study found something else that matters for race day: heat doesn't just slow runners down. It changes how they slow down.

In cooler conditions, more runners successfully hold an even pace or run a negative split (second half faster than the first). As temperatures rise, the proportion of runners who positive split, meaning they slow significantly in the second half, increases across all age groups.

A 2022 study in Sport Sciences for Health confirmed this pattern. Heat stress and pacing errors compound each other. Runners who go out too fast in the heat face a double penalty: they generate extra metabolic heat from the faster pace, and their cooling systems are already under strain from the environment. The result is often a dramatic fade in the final 10K.

For older runners, this effect is amplified. The NYC Marathon data showed that the shift toward positive splitting in heat was more extreme in older age groups. A 50-year-old runner on a warm day is statistically much more likely to fade in the second half than a 25-year-old on the same day.

What Is the Ideal Temperature for Running a Marathon?

Research across multiple major marathons, including a large-scale study of the Berlin Marathon published in Frontiers in Physiology (2021), consistently points to the same range. The optimal wet bulb globe temperature (WBGT) for marathon performance is between 5 and 10 degrees Celsius, with peak performance around 7.5 degrees Celsius.

Above that optimal range, performance drops for everyone. But the rate of decline is not the same across groups. Research on endurance events shows that slower runners lose 1.5 to 3.2 percent for each 5 degree Celsius increase in WBGT, while faster runners lose less. Since older runners tend to have longer finish times, they face both the age-based thermoregulation penalty and the duration-based exposure penalty at the same time.

How Should Older Runners Adjust Their Race Plan for Heat?

The NYC Marathon data, combined with the broader thermoregulation research, points to a few practical changes for runners over 30 racing in warm conditions:

1. Start slower than you think you need to. The research shows that positive splitting increases dramatically in heat, especially for older runners. A heat-adjusted pace calculator can help you set a realistic target. Starting 5 to 10 seconds per mile slower than your cool-weather pace in temperatures above 15 degrees Celsius WBGT is supported by the data.
2. Add an age adjustment on top of the heat adjustment. If a general heat adjustment formula says to slow down by 3%, an older runner should consider adding another 1 to 2% on top of that. The NYC Marathon data shows the heat effect is not uniform across ages. Your age-adjusted training plan should account for this.
3. Front-load your hydration and cooling. Because thermoregulatory responses are slower in older athletes, pre-cooling strategies (cold towels, ice vest during warmup) and aggressive early hydration are more important than for younger runners. Don't wait until you feel thirsty.
4. Shift your goal from time to effort. On a genuinely hot day, your VDOT-based race prediction made in cool conditions is no longer valid. Running by perceived effort or heart rate rather than pace prevents the cascading failure that the pacing data reveals.
5. Plan your race nutrition for heat. Higher core temperatures accelerate glycogen depletion. In the heat, you need more calories and more fluids per hour than in cool conditions. This is even more true for older runners whose cooling systems are working harder.

References

• Knechtle, B. et al. (2022). "The Influence of Environmental Conditions on Pacing in Age Group Marathoners Competing in the New York City Marathon." Frontiers in Physiology. PMC.
• Wallett, J. & Periard, J. (2021). "Temperature regulation during exercise in the heat: Insights for the aging athlete." Journal of Science and Medicine in Sport. PMC.
• El Helou, N. et al. (2012). "Impact of Environmental Parameters on Marathon Running Performance." PLoS ONE. Analysis of optimal WBGT range for marathon performance.
• Maffetone, P. & Laursen, P. (2020). "The Role of Environmental Conditions on Master Marathon Running Performance in 1,280,557 Finishers the New York City Marathon From 1970 to 2019." Frontiers in Physiology. PMC.
• Weiss, M. et al. (2022). "Pacing and heat stress independently and differentially effect elite marathon performance." Sport Sciences for Health. Springer.
• Knechtle, B. et al. (2021). "Trends in Weather Conditions and Performance by Age Groups Over the History of the Berlin Marathon." Frontiers in Physiology. Frontiers.
• Kenny, G. & Flouris, A. (2018). "Aging and Thermoregulatory Control: The Clinical Implications of Exercising under Heat Stress in Older Individuals." Journal of Aging Research. PMC.