The word endurance can be a tricky one to define: it is both physical and psychological. Many of the research studies carried out on physical endurance in the twentieth century have reached the same conclusion. In the same way as a car with a stuck accelerator pedal will keep going until it runs out of fuel or the radiator burns out, so will a human being continue to keep pushing on until something breaks. At the beginning, researchers were mainly focussed on understanding VO2 max, that is, the maximum amount of oxygen that the body can absorb and use during physical exertion. A high VO2 max value indicates that the heart, lungs, and muscles are working at optimum levels to supply oxygen to muscle tissues, and thus ensure better performance. Another aspect that researchers have focused on to define physical endurance is the lactic threshold, also called anaerobic threshold. This term describes the point at which the body begins to produce lactic acid faster than it can burn it.
With this in mind, the advent of new and sophisticated techniques for measuring and manipulating the brain has changed the way we look at endurance. Scientific experiments have shown that human resistance also strongly depends on how the brain interprets the danger signals that the body sends it. In fact, the brain carries out an important regulatory function during exercise, because it prevents excessive effort, which if not contained, can ultimately lead to death.
Henry Worsley's Expedition to the Edge is a great example of how bad things can get when the brain stops functioning properly. In 2015, the former British army officer decided to cross Antarctica on foot, alone, with the aim of completing the same route as the great explorer Ernest Shackleton. After 56 days of walking, bad indigestion prevented him from sleeping when he stopped to rest. The next day, instead of resting, Worsley decided to continue his journey as planned, and take on the Titan Dome, a 3100 metre high ice dome. Worsley wasn’t very concerned about his physical condition because he knew that he could call for help with a satellite phone, and if necessary, would be rescued within a few hours. However, his confidence proved fatal, because it caused him to underestimate the limitations of his body. Increasingly exhausted, but determined to complete the crossing, Worsley continued walking for another week. Finally, just under 50 kilometres from the finish line at the edge of the Ross Ice Shelf, he was forced to give up. He was taken to the hospital in Punta Arenas, Chile, where the doctors diagnosed him with bacterial peritonitis and an abdominal infection which, just a few days later, led to his premature death. His body had become too weak to react.