The Ultimate Limit of Human Endurance

Whether it’s hitting the wall in a marathon, or competing at top level sport, many of us have had times where it feels like we've reached the max of our bodies capabilities. But, when it comes to endurance sport, where does the true limit of human endurance lie? Recent research done by scientists at Duke University has just found out... 

The answer? 2.5 times the body's resting metabolic rate, or 4,000 calories a day for an average person. Anything more than this would be unsustainable. 

Scientists studied various endurance activities including triathlons, the Tour de France, arctic trekking, and the 140-day transcontinental Race Across the USA (where athletes ran 3,080 miles from California to Washington DC in 140 days). 

They found a pattern between the length of the event and energy expenditure, which showed that the longer the event was, the harder it was to burn through calories. Energy use would start off high, but eventually, level off at 2.5 times the resting metabolic rate. This means people can go far beyond this when doing it in short bursts (such as in a triathlon or marathon), but when it comes to long term endurance, this is simply unsustainable. Interestingly, they also discovered that pregnant women live at nearly the limit of what the body can cope with – the ultimate endurance test!

So, if running a marathon felt like you'd completed the ultimate endurance test, we're sorry to tell you that this isn’t quite the case... In fact:

• Marathon (just the one) runners used 15.6 times their resting metabolic rate

• Cyclists during the 23 days of the Tour de France used 4.9 times their resting metabolic rate

• A 95-day Antarctic trekker used 3.5 times the resting metabolic rate

Want to read the full study? Find it from Science Advances, here.