Mike Tyson glares at the members of the boxing gym. Tyson’s tattooed face is printed on a poster, hung high on one wall, alongside the quotation: “Everyone has a plan until they get punched in the face.”

Below the poster, a big wooden door swings open, and Jacob Clark, 17, steps into the gym, exhaling puffs of steam. It’s his first day or training. Based on Tyson’s wise words, Clark is already one step ahead of the game: he plans to learn how to take a punch or two, and to give some back as well.

A gust of winter air follows him in from Main Street, and five men in exercise clothing glance up at him. Two of them are sitting on the floor, their legs stretched out to either side. Another two are warming up on the punching bags that line one wall. The fifth man, instructor Aaron Snow, puts down a clipboard and walks over to Clark, his arm extended. “Hey man,” he says. “How’s it going?”

Snow takes pride in his Sitmangpong Thai Boxing & MMA gym — a club that opened in Greenfield in 2014 before moving to Millers Falls this past November — not only because it’s a great workout, but because he sees it as preparation for a healthy, strong life.

Boxing and martial arts are sports that strengthen the body, but also something deeper down, closer to the core. As Snow puts it: “Hand to hand combat is the purest form of competition in the world. It’s truly life-changing to get into the ring and put yourself on the line with someone who is trained to defend themselves.”

Snow teaches Muay Thai, a boxing style that originated in Thailand, but which has become popular internationally over the past decade, thanks mainly to action movies by Thai stars like Tony Jaa (Ong Bak) and the rise of televised competitive mixed martial arts (MMA).

Muay Thai means “the art of eight limbs” because fighters use not only their fists and feet to land blows, but also their elbows, knees, and shins. It’s good cardio and stress release, but it’s also a “realistic” fighting style, as Snow put it. “There’s not a lot of striking the air or hitting imaginary opponents. It’s very much full-force, all the time.”

Clark, who lives in nearby Erving, explains to Snow that although he’s played football and tried out karate, he’s never trained in Muay Thai.

“You don’t have to be hit by anybody if you don’t want to,” Snow tells him. “Everything here is optional. Nobody here is forced to spar.”

This is a one-hour Muay Thai fundamentals class — taught on Mondays, Tuesdays, and Saturdays — a self-paced but intense workout designed to develop proper fighting techniques.

“Don’t worry, we’ll get you tired in an hour,” Snow says with a smile, clapping Clark on the back. Then he turns to the others. “It’s going to be super-basics today, guys.”

Clark is a quick study. And according to Snow, whom I spoke with on the phone later in the week, the newbie has been coming back for more classes.

“My philosophy is: no one gets left behind,” Snow said. “People who want to work only on themselves just don’t fit in here.”

Snow, 32, grew up in a boxing family: his father, uncle, brothers, and grandfather all practiced the art of the punch. Growing up, his favorite movie was Kickboxer, starring Jean-Claude Van Damme.

As a teenager fascinated by the art of hand-to-hand combat, he branched out and tried Muay Thai. “It’s becoming more of a household name, but when I started learning this 15 years ago, nobody knew what this was,” he explained. “They’d say: Muay Thai? Isn’t that a drink?”

But Snow kept at it. He has taught at several MMA gyms in the area and trained with three world champions from Thailand: Saekson Janjira, Coban Lookchaomaesaitong, and Samart Payakaroon. One month into his new arrangement in Millers Falls, he seems pleased with the larger space.

For a new student to join the Sitmangpong club, they must be accepted in by Snow and by current students. Over the next few weeks Snow will be looking into expanding the gym into the space next door — which would allow him to install the full-size boxing ring he currently maintains at his home — but right now he can manage about 40 students for classes six days a week. Currently, the headcount is pretty close to that.

Snow says the club offers the only all-women MMA class in the area, taught by members Erica McIntyre and Laura Harcourt, on Thursday evenings. Club members also fight competitively each month at regional MMA, Muay Thai, and boxing events. Five of Snow’s students — four men and one woman — will participate in matches on Jan. 23 in Connecticut and on Feb. 6 in Boston.

Most of his students that go to matches didn’t walk in on their first day wanting to fight competitively, “but once they drill and learn and see how good they’re getting, they start to get interested.”

The Sitmangpong Thai Boxing & MMA gym doesn’t pay Snow’s bills. He works a full-time administrative job in Amherst to support himself, his wife, and his four children. The gym stays open thanks to dues paid by club members, which go toward rent, utilities, equipment, and travel for competitions.

“This is not a job, by any means, and the club is not a business,” he insisted. “Our goal isn’t to make money — it’s to spread a love of Muay Thai in Western Mass.”

“I get to do my favorite thing in the world, spend time with my family, and be part of a group that values hanging out and getting fit,” he added. “I’m seriously one of the luckiest guys in the world.”

Six heavy punching bags, plus a ball-shaped double end bag, take up nearly a quarter of this open, but fairly small gym space. American and Thai flags hang on the far wall. The floor is padded. Next to a couch sits a mini fridge stocked with bottled water.

As the men stretch, they chat about recent televised fights. Then Snow brings Clark to a full-length mirror. While the others shadowbox, these two work through basic punches.

“Feet side by side,” Snow says, and Clark follows along. “From here, you’re going to keep your chin tucked in and your shoulders up. Bring your hands up so they’re about five or six inches in front of your face.”

When Snow does this, the Thai letters tattooed onto his forearms reflect in the mirror (these words are the name of Snow’s gym, which translates roughly to “scorpion club”). “You want your palms facing each other, and your arms vertical,” Snow says. “Next we get on the balls of our feet, so that we can rock our weight between our hips. We’re constantly moving, to make it harder to see what we’re going to throw. If you stand like a statue, it becomes obvious.”

They run through jabs (“use your hips”), then double punches. Clark learns to guard his face with his back hand held high, like he’s holding a phone to his ear. He drills this while Snow checks in on the other athletes, shouting “Nice work, brother, nice technique!” and “Step it up, there we go! Let’s see it, fellas!”

The class spends the final 30 minutes on kicks. As he whacks away at a heavy bag, Clark learns to think of his right arm and right leg like a pair of scissors. Pivot your hips, kick forward, and pull your arm back for extra torque. The thick, satisfying whap! from the bag says it all: practice makes power.•

Contact Hunter Styles at hstyles@valleyadvocate.com.