Six marathons a week? Scientists reveal the limit of human endurance

Scientists have calculated an ‘ultimate endurance limit’ - how much energy a person can healthily use every day - through analysing participants of multiple elite events.

The study began by looking at Race Across the USA, an event where athletes run from California to Washington, covering a total of 3,080 miles in 140 days.  Participants were running six marathons a week for months.  They also monitored cyclists in the Tour de France and an Antarctic trekker.

The results were published in Science Advances and concluded that using 2.5 the body’s resting metabolic rate was the limit; anything above this could not be sustained long term. To contextualise this, in a marathon, runners use 15.6 times their resting metabolic rate, and cyclists used 4.9 times theirs, for the 23 days of the competition.

This indicates that although you can perform high intensity exercise such as a marathon, your long-term endurance will not build up past this limit regardless of your training: even the fittest person cannot run marathons daily without problems arising.

Dr Pontzer, who worked on the research, highlighted its use for athletes: “knowing where your ceiling is allows you to pace yourself smartly… it is most applicable to training regimes and thinking whether they fit with the long-term metabolic limits of the body”.

Other things of note in the research include that pregnant women are functioning at 2.2 times their resting metabolic rate, making them close to pro-athletes in terms of endurance.  It is also suggested that the cap is because of the human digestive system; it may be that we are not able to digest food at a rate that would fuel us for anything more intense.

Medicine applicants might be interested in how this information might relate to healthcare for very active individuals, and what this might reveal to us about the digestive system and the metabolic system.