At an hour when lampposts carve shadows over empty streets, when geese outnumber people on the Esplanade, skunks troll through Brookline, and rats prowl around Beacon Hill, Tom Goulet is out sweating, his muscles burning, his mind far from shutting down.
Which for most people, given the time and his obligation to be up for work at dawn, would be the logical thing for the mind to be doing.
Nearly every night of the week, come rain, snow, or howling winds, the 48-year-old venture capitalist from the North End laces up his sneakers, tucks a cellphone in a fanny pack, and joins an unallied cabal of midnight runners.
"It's almost as peaceful as sleeping," says Goulet, a father of three. He says he often sees dozens of other late-night joggers but on a recent midnight run seemed to have the city to himself. "It's really beautiful to be out here on your own. It's nice and strange to feel the stillness of the city. It feels like a postcard."
Goulet and his seemingly cracked comrades in reflective shoes say they're aware of the risks close encounters with menacing denizens of the dark, or drivers failing to spot them darting through intersections, or anything from slipping on black ice to turning an ankle in an unseen pothole.
They also don't heed the advice of the American Academy of Sleep Medicine, which counsels people to avoid strenuous exercise for as much as six hours before sleep.
"The idea is to prevent the body from producing endorphins and stimulants that can disturb sleep or lead you to wake up in the middle of the night," says Kathleen McCann, an academy spokeswoman. "Increased levels of hypocretin resulting from exercise at night can lead to awakenings at night."
Some scholars who have studied late-night exercise take exception to the academy's advice. They argue that people such as researchers, graduate students, and medical professionals who work irregular schedules in short, many people in the area are better off running late at night, when it's often most convenient.
Shawn D. Youngstedt, an assistant professor in the department of exercise science at the University of South Carolina, has overseen two studies that found late-night exercise does not impair sleep. In some cases, he says, it even helps.
One of his studies, published in the journal Physiology and Behavior in 1998, found that of a dozen college students who exercised on a stationary bicycle for an hour a half-hour before bed, none had trouble falling asleep. The other study, published a year later in the journal Medicine and Science in Sports and Exercise, found that of 18 college students who rode a stationary bicycle for three hours a half-hour before sleep, none had problems sleeping.
Lucas Woodward's most serene runs usually come after midnight, often in the dead of winter just after a snowstorm. With few cars on the road and a heavy stillness in the dry air, he says, there's something transporting about the quiet, especially after a long day.
The 22-year-old computer technician from Jamaica Plain often jogs around Jamaica Pond late at night, when it is pitch black save the distant streetlights and the odd car in the distance.
"At night, the wind dies down, and when you're all alone you can hear every footstep," says Woodward, who, like Goulet and other midnight runners, says he has no trouble falling sleeping afterward. "It's really peaceful."
But running in the middle of the night can have its awkward moments, particularly in Boston.
Their company, aside from nocturnal animals, occasionally includes drunken students spilling out of bars from the Back Bay to Brighton. There's also the homeless, who tend to stare at late-night runners as if they're creatures from another planet, and the cars that slow down, their passengers ogling the odd characters coursing through the dark. Even cats wandering the streets stop and gaze at those intruding on their solitude.
"It's socially unacceptable to exercise at night," says Woodward, a recent Boston University graduate who doesn't worry about lurking danger. "People look at me with the strangest expressions, but I feel like I can outrun anyone."
Some runners say they understand the allure of jogging late at night, when the streets are so empty that it feels safe enough to run in the middle of the road. But they advise against it.
Four-time Boston Marathon winner Bill Rodgers has run several late-night races, including midnight dashes through Sao Paulo, Brazil, and champagne-strewn courses in Manhattan's Central Park. For competitors, he says, it's usually best to run early in the morning, when muscles have had a chance to rest.
"At the end of the day, your body wants to rest," says Rodgers, 58. "It's also a lot easier to trip at night."
When Hal Higdon served in the Army 50 years ago in Germany, he often ran through the Black Forest at night, the moon his only light. The 74-year-old veteran of 18 Boston Marathons and author of "Boston: A Century of Running" says he now prefers to run under the sun. "Safety is a serious issue," he says, urging night runners to keep their iPods at home.
Others argue that it's safer to run at night, particularly during the summer or in warmer climes.
For Bob Loewenthal, a 73-year-old retired attorney from Atlanta, there are certain times of the year when running in the day is too dangerous. In the summer, when the temperature soars above 90 degrees, he starts his long runs around 3 a.m.
"During the day, I can have running company; I can see where I'm going; I can watch the scenery; I don't have to adjust my meal and sleeping schedule," he says. "Unfortunately . . . I must start a long run at the time that everyone else is sleeping in order to avoid the heat."
On a recent night in Boston, heat isn't the problem. With cold, stiff winds blowing off the Charles, Dan Laskey and Matt Webster lumber through Brookline toward the river, the lights of the skyline melting into the dark water.
At 12:30 a.m., their faces flushed less than a mile into the run, the 22-year-old roommates from Boston are wide awake. Morning, when they both have to be at work, seems far away.
"It's a good way to end the day," Laskey says.
Webster adds: "It beats watching TV."
Then the two disappear into the night, the reflective decals on their shoes slowly fading in the pale moonlight.
David Abel can be reached at email@example.com. Follow him on Twitter @davabel.