“You’re just burning a lot of fuel,” he said.

Chinese History professor Michael A. Szonyi, who has been on sabbatical leave this past year to write a book about 14th-century Chinese soldiers, said he has run on several continents in preparation for the marathon.

“Basically I coordinate all of my travel with my running,” he said. “Three weeks ago I ran in London, Ontario, and it was -28 degrees centigrade. I was running in ski goggles and ski gloves. Then I got on the plane and went to Singapore, where I ran. It was 34 degrees centigrade.”

Szonyi also said his book is often a topic of conversation when he runs with other people.

“I’ve explained it to a physiotherapist on a three-hour run, to an accountant on a four-hour run,” Szonyi said, laughing. “I think the book will be a better book. I’ve been with a wider audience.”

Terah E. Lyons ’14 pinched a metatarsal nerve while training and has since been swimming, biking, and lifting weights to keep in shape for the marathon. Although she hasn't run distance recently, she said cross training has kept her busy.

“Training for a marathon is a different animal,” Lyons said. “It definitely takes a lot of time.”

‘A FUNDAMENTALLY HUMAN BEHAVIOR’

For some, running is a stress relief from hectic life in the Harvard bubble. For others, it promises the challenge of overcoming physical pain, or the intimacy of a close-knit running community. For those who will participate in Monday’s marathon, that symbolism will not go unrecognized.

Lieberman, who has studied the evolution of running in humans, said running is a “fundamentally human behavior.”

“We’ve been doing this for millions of years,” he said.

Like the ancient humans he studies, Lieberman sometimes trains barefoot, though he said he will not be running the Boston Marathon barefoot. To him, the best part of running marathons is the feeling of achievement he receives after pushing through a grueling 26.2 miles.

“There’s point in every marathon, where it’s about strength and the ability to overcome, because you’re tired and you're hurt and wonder why you're doing this,” he said. “ That’s what’s so incredible about it.”

Mollerus, also an avid rockclimber, became motivated to run during his junior year of high school, after he fell 35 feet during a national rock climbing competition. He shattered two vertebrae, which impeded him from climbing, but he said that didn’t stop him from finding another athletic outlet.

“I just really like movement,” he said. Mollerus added that he hopes to beat his father’s marathon time on Monday. Mollerus found out recently that he will be the youngest runner in this year’s race.