Photo by Miguel A Amutio (Unsplash)

Marathon popularity has been growing unstoppable during the last years, at least until the Covid-19 appearance, that has casted a shadow over a booming business.

With such levels of practice have appeared also some health problems, including injuries, hyponatremia, kidney and liver malfunction, gastrointestinal issues and, in some cases, even sudden death.

Therefore, the increased interest among scientist to investigate physiological changes associated with marathon performance. That is the goal of the research article pointed out in our post.


The study

Twenty experienced amateur male marathon runners participating in the Shanghai International Marathon took part in the study. They didn´t have previous health problems. Blood samples were collected at fasting, the morning of the day before the marathon, and within 1 hour after completion.


The results

Creatine kinase is a protein whose levels are related with fatigue, and usually increase during infections or injuries. Its levels increased after the marathon, indicating a certain degree of cardiac and muscle damage.

During long-term exercise the energy supply from the carbohydrates reserves becomes insufficient for the race´s demands. It is the time to start mobilising the fatty acid depots as energy source. They are the basic component of the lipids, or “fat” of our bodies. The whole process is called lipolysis, and involves activation of the tricarboxylic acids cycle, or TAC, an important pathway to provide energy during long-term exercise.

Pyruvic acid is an intermediate product of the metabolism of carbohydrates, lipids and proteins, playing an important role in the energy metabolism. Because of the activation of the TCA cycle with exercise, pyruvic acid levels consequently increased after the race, showing that the use of fatty acids was increased during the marathon run.

Glucosamine is an important substance responsible of the structure of joints and cartilages. Its levels decrease with aging, especially when there is deterioration of joints function. Long-tern exercise was shown to cause inflammation with a reduction in glucosamine levels. Therefore, the common recommendation of exogenous glucosamine for long-distance runners (abundant in shelled seafood).

Cortisol manages how your body uses carbohydrates, fats, and proteins, among other important functions. Blood levels of cortisol are indicators of functional status. Cortisol is produced under stress and strenuous exercise, with an elevation of its levels with moderate to high-intensity exercise (>60% VO2max). There was a significant increase after running the marathon.

Testosterone levels are related with the physical abilities during resting conditions. Its levels are usually reduced after exercise. It is what happened with runners after the marathon.

On the contrary caffeine metabolism was also activated because of an increase in the levels of theophylline and theobromine in blood. This activation would help mobilize fatty acids deposits and induce lipolysis. The craziness for marathon, reaching even addiction levels in many, would have a chemical origin, because of an enhancement in the caffeine metabolism.



  • Marathon activated the TAC cycle to increase energy supply for the runners, by enhancing the utilization of lipids and amino acids, besides the carbohydrates.
  • Levels of cortisol and testosterone could be used to determine working load and physical capabilities.
  • The increase in the levels of caffeine metabolites (theophylline and theobromine) following exercise indicates an enhancement on the lipid metabolism and may explain the “addiction” to exercise.



Runners’ metabolomic changes following marathon.

Shi R, Zhang J, Fang B, Tian X, Feng Y, Cheng Z, Fu Z, Zhang J, Wu J.

Nutr Metab (Lond). 2020 Mar 13;1 7:19. doi: 10.1186/s12986-020-00436-0.

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