French triathlete Cassandre Beaugrand exhausted after the end of a race
Elite athletes can push their bodies to their maximum limits, but even they cannot overcome the boundaries of human nature.
A new study has found evidence that, regardless of physical form or a person’s training, the human body is limited and cannot burn calories at a more than 2.5 times your metabolic rate at rest for long periods of time.
According to the authors of , recently published in Current Biologyexceed this rate over more than 30 weeks of training it’s not impossible, but it’s rare.
A previous one, published in 2019 in Science Advanceshad already identified a “metabolic ceiling” similar for human resistance, located approximately in the 2.5 times the metabolic rate at rest.
However, the new investigation used a reference measurement for calorie burning and analyzed twice as many athletes compared to previous studies.
The analysis focused on 14 world-class athleteshighly trained, including runners, cyclists and triathletes. Only two athletes were women, and the majority were between 30 and 44 years old.
First, researchers calculated the total energy expenditure of participants to determine how many calories they burned in each workout and during competitions.
Then, says the , participants drank a bottle of water enriched with two metabolic tracers, whose levels could be measured in urine and used to predict the energy expended during exercise.
This equation was then used to predict maximum “metabolic reach” of each individual over 52 weeks, based on detailed training records. On average, the athletes in this study rarely burned more than 4,000 calories per day, which corresponds to 2.4 times your resting metabolic rate.
For short periods, athletes were able to exceed this rate. The maximum metabolic range recorded was more than seven times the basal metabolic rate of the athlete, measured during a race lasting almost 24 hours in a trail of mountain.
Some ultramarathoners have also exceeded more than four times their basal metabolic rate in certain multi-day races. But when calculated over a year, these energy spikes were short-lived.
The human body may occasionally burn more than 2.4 times your basal metabolic rate, but after approximately 30 weeks of training and competitions, it is unlikely that it will exceed this average ceiling.
Only four athletes in the study exceeded this ceiling predicted metabolic rate after 30 weeks or more, but they are exceptions, and the difference was small. His metabolic range was around 2.7 times the resting rate.
“The athletes in this study did not significantly exceed the proposed metabolic ceiling,” the authors conclude. “World record ultra-endurance running performances suggest significantly higher energy expenditure may be possible in exceptional cases”.
But without direct measurements of a larger number of elite athletes, the limits of human endurance remain, at best, unclear. Growing evidence suggests that there is a hard limit for extremes of human resistance, but there is always the possibility of an athlete emerging in the future who will challenge him.
