More Than 55,000 Runners Prepare for the 48th Chicago Marathon

On October 11th, Chicago is going to stop to get moving. More than 55,000 runners from around the world will take to the streets of 29 neighborhoods in the 48th edition of one of the fastest and most beloved marathons in the global circuit. From Kenyans and Ethiopians fighting to break time barriers to the everyday runner who has trained for two years to finish their first 42K, everyone will share the same asphalt on the same Sunday. And that, in a sport as individual as running, is the prettiest part of the story.

The Context

The Chicago Marathon is one of six races that make up the Abbott World Marathon Majors, the most prestigious road running circuit alongside Boston, London, Berlin, New York, and Tokyo. It's no accident that it's there: its course is practically flat, with few sharp turns and climatic conditions that in October tend to be cool and favorable. That combination historically made it one of the fastest tracks in the world, where world records have fallen on more than one occasion.

But reducing Chicago to a record number would be unfair. What makes this marathon special is its route: a postcard in motion that crosses neighborhoods as diverse as Pilsen, Chinatown, Boystown, and Wicker Park, with crowds that—according to those who've run it—don't leave a single kilometer in silence. For the elite runner it's an opportunity to set a time; for the everyday runner, it's a party of endurance and community that lasts more than four hours in most cases.

With a field of 55,000 people, the logistics behind it are enormous: staggered starting corrals, hydration stations every few kilometers, and a medical system designed for a city that, for one day, multiplies its population running.

What the Science Says

Running 42.195 km isn't just a matter of willpower; it's pure physiology, and recent science has plenty to say about what happens in the bodies of those 55,000 runners.

First, the pacing question. An analysis on pace variability in marathons (Cuk et al., 2024) showed that the most successful runners are those who maintain a more consistent pace, avoiding the classic "start fast and suffer later." This relates directly to fatigue: a review on fatigue development in self-paced exercise (Azevedo et al., 2021) explains that perceived exertion escalates in a non-linear way, and that trained runners learn to "read" those signals better than beginners, adjusting their pace before it's too late.

There are also interesting differences between genders in how effort is distributed. A study on pacing in women and men in marathon and half-marathon races (Nikolaidis et al., 2019) found that women tend to manage a more moderate pace drop in the second half of the race compared to men, something linked to metabolic differences and decision-making during exertion, topics also addressed in a broader review on sex differences in endurance running (Besson et al., 2022).

Finally, nutrition during the race is a separate chapter. A recent review on carbohydrate strategies in elite endurance (Cao et al., 2025) confirms what we already knew but continues to be underestimated by the amateur runner: adequate carbohydrate intake during prolonged exertion delays fatigue and sustains pace in the final kilometers, precisely where races are won or lost.

What It Means for You

You don't need to be elite to apply these lessons on the day of your next marathon, whether in Chicago or your own city:

• Start with a cool head. The euphoria at the starting line is the main culprit behind breakdowns at kilometer 30. An even pace, even slightly conservative at the start, usually performs better than a fast opening.
• Plan your nutrition, don't improvise it. Practice in your long training runs how much and how often you're going to consume carbohydrates. Race day is not the time to experiment.
• Listen to fatigue signals, but don't fear them. It's normal to feel the effort getting harder from the halfway point; the key is differentiating expected fatigue from a real alarm signal.
• Add strength to your routine. Strength training improves running economy even in a fatigued state, something crucial to sustaining pace in the final kilometers of a marathon.

Chicago will be, once again, a showcase of the best of worldwide running. But it's also a reminder that, no matter what time you run, crossing that finish line is a victory built with science, patience, and kilometers of preparation.

References

• Cuk I, Markovic S, Weiss K. "Running Variability in Marathon-Evaluation of the Pacing Variables." Medicina (Kaunas), 2024. https://pubmed.ncbi.nlm.nih.gov/38399506/
• Azevedo RA, Silva-Cavalcante MD, Lima-Silva AE. "Fatigue development and perceived response during self-paced endurance exercise: state-of-the-art review." Eur J Appl Physiol, 2021. https://pubmed.ncbi.nlm.nih.gov/33389141/
• Nikolaidis PT, Ćuk I, Knechtle B. "Pacing of Women and Men in Half-Marathon and Marathon Races." Medicina (Kaunas), 2019. https