After extensive study of various endurance events, the Duke University finally discovered that the average human body’s endurance threshold is at 4,000 calories a day. Anything beyond that will eventually be arduous to sustain.

Duke University began the study Race Across the USA, an event that required competers to run from California to Washington DC. The race covered 3,080 miles and was to be finished in 140 days.

The researchers investigated the effect of race on the athletes’ bodies. The calories they burned for the whole duration of the race and their resting metabolic rate pre and post race were also recorded. The resting metabolic rate refers to the number of calories burned when the body is relaxing.

The results of the study showed that at the onset of the race, the use of energy was high but it eventually stabilized at 2.5 times the resting metabolic rate. It likewise revealed that the longer the event, the more difficult it is to burn through the calories.

During a marathon, athletes used 15.6 times their resting metabolic rate, while those who cycled in the 23-day Tour de France exerted 4.9 times their resting metabolic rate. 95-days of trekking the Antarctica use 3.5 times the resting metabolic rate.

The researchers argue that the cap may be ascribed more to our digestive system than any other organ in the body.

They discovered that the body cannot undergo its usual digestive function to endure more extreme energy use.

In shorter events, the body can use up its own reserves and recover it shortly afterward. However with longer events, the body to level off its energy use.

The researchers believe that these findings would be of help to athletes especially during their training regimens and deciding on the appropriate races they should compete in.