Running a marathon is a huge life accomplishment, and though it has become quite popular over the past few years, it's still a pretty small number compared to the rest of the United States. The run had its peak year in the United States with 541,000 people crossing the finish line in 2013. But why would anyone want to run a marathon in the first place? It takes a whole day to complete the 26 miles (unless you're Dennis Kimetto of Kenya, who can do it in just over two hours); not to mention it's painful and tiring. Yet, some people decide to go back and do it again. But why?

BPS reports that people forget how painful the experience was for them. Przemyslaw Bąbel conducted a study where he interviewed 62 runners after the 11th Cracovia Marathon in Kracow, Poland in 2012. Moments after passing the finish line they got the opportunity to answer a series of questions about “the intensity of the pain they were in, its unpleasantness, and the positive and negative emotions they were feeling.” Runners reported feeling and average of 5.5 on a seven-point pain scale.

Babel then waited six months until he contacted the participants to ask them the same questions about the marathon. Turns out the participants' memories about the pain they endured wasn't that sharp. Six months later runners remembered the pain being around 3.2 on the seven-point pain scale. Indeed, “participants underestimated both recalled pain intensity and unpleasantness.”

However, he noted that the majority of runners that underestimated their pain looked back at the marathon as a positive experience. But those who suffered more or looked back at the memory as a negative experience recalled more feelings of unpleasantness and pain. This insight has led Babel to suggest that “pain induced by physical exercise is not remembered accurately and the pain and negative effect experienced influence recall.”

As NYU psychology professor Joseph Ledoux explains, memories are products of neurons firing in your brain, and since neural networks are constantly forming anew, memories change dramatically over time. Rather than recall a single event accurately, memories change over time based on how we recall our prior memory of the event.

Read more about the study of pain and memory at BPS.

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