Inside the Body of a Marathon Runner

By Vivienne Couris, C2ST Intern, DePaul University

The 2023 Boston Marathon recently concluded when thousands of highly trained runners crossed the finish line after a grueling 26.2 miles. Evans Chebet, the winning runner, completed the race in an impressive 2 hours, 5 minutes, and 54 seconds for an average pace of 4 minutes and 48 seconds per mile! 

Extraordinary athletes like Chebet have trained their bodies to carry out several biological processes with incredible efficiency, allowing them to run a race most people wouldn’t even fathom running in their lifetimes. In this post, we’ll take a closer look into some of these amazing adaptations.

When a runner begins a marathon, their body begins to do what most of our bodies do when they exercise: breathing quickens, the heart pumps faster, and the body produces sweat. These processes are utilized to keep the body from overheating and to provide muscles with the oxygen they need to continue working. Elite runners, however, are able to take in much more oxygen than the average human. This amount is known as the Vo2 max. The higher your Vo2 max, the more efficient your body is at using oxygen. Elite runners have conditioned their Vo2 max to be up to 165% higher than that of non-runners (2)!

The heart muscles of marathon runners also tend to be quite different when compared to those of non-runners. Elite runners’ hearts have adapted thicker walls, particularly around the lower chamber, to help facilitate stronger pumping of blood, as well as a greater overall amount of blood to the muscles. This is known as stroke volume, and the top endurance athletes in the world have an average stroke volume that is 67% higher than that of regular folks’ (4). 

A marathon runner also needs a high lactate threshold, which refers to the ability to keep lactate from accumulating too densely in the blood. Lactate, or lactic acid, is an ever-present byproduct in the bloodstream, produced from red blood cells and muscle cells (5). Exercise, however, dramatically increases its concentration, and too much can lead to extreme fatigue (3). Marathon runners have gained a higher lactate “threshold” through their training, meaning their body is able to more efficiently deal with lactic acid and keep their muscles from getting tired too quickly (2). 

Finally, marathon runners must use certain supplements during their run to maintain energy and give their body what it needs to continue moving. All of the adaptations we discussed above require massive amounts of energy to carry out, and cause immense loss of water, minerals, and food sources stored within the body. Marathoners, therefore, must use a wide array of products to help with this issue (1). Specialized liquids often contain electrolytes and water, which are important to regulate muscle function and keep the body hydrated despite lots of sweating. Gels are another popular nutritive source during endurance runs; they typically contain easily digested carbohydrates and amino-acid chains. This helps the body to restore its glycogen (muscle energy source) stores and prevent soreness. Dried fruits or even certain candies are also popular among endurance runners for the same reasons (6). 

Overall, marathon runners’ bodies have adapted mind blowing physiological characteristics to help them race such a long distance. It takes about six months for the average person to train for a marathon, and many years of special training to become an elite runner. VO2 max, stroke volume, lactate threshold, and energy absorption are only a few of the insane processes one builds up and improves as they train. Next time you see a marathon runner, or even go for a casual run yourself, take a moment to appreciate what an incredible work of nature the human body is!


  2. The-physiology-of-elite-runners

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