ith its bold colors and lettering, the sign outside Kostas Argiropoulos's boxing gym looks as if it might be announcing a carnival act. Instead, it cries, "Beginners Welcome!" And beginners, you should indeed feel welcome. In this unassuming space in Jamaica Plain, people at all levels of fitness can learn boxing basics from a guy who not only is an expert, but has a contagious zest for life.

Three decades ago, Argiropoulos opened his doors to any and everyone interested in training like a boxer. Nestled beside his house on the corner of Paul Gore Street and Chestnut Avenue, his tiny gym could house two cars if it wasn't already filled by four heavy bags, two speed bags, a dozen jump ropes, medicine balls, mats, and several of his own wood carvings. It's here that, six days each week, he runs people through his boxer's workout.

Though in a residential neighborhood, the gym isn't too hard to find. When I heard loud disco music and a steady stream of positive exclamations uttered with a Greek accent coming from the lot on the corner, I figured I was close. "Yeah, good! Just like that. Good stuff, yeah?" Argiropoulos shouts while flitting from boxer to boxer, encouraging them to "twist the body" or "snap the arm" as they throw punches.

I push a set of Velcro tent flaps aside and step into the gym. It's a chilly morning and an ancient space heater thumps out a hot breeze from the corner. After I give Argiropoulos an idea of the kind of workout I'm interested in, he leads me over to the jump ropes and explains how the session will go. As a first-timer, I'll be working with him directly. "You sit in front of a computer all day?" he asks me. "This will help make you feel"—he spreads his arms apart and rises up on his tiptoes, then quickly exhales and brings his hands to his heart—"feel good. It'll clear all that stuff outta your head." Around me, others go about the gym on their own, one holding hand weights while throwing punches toward a mirrored wall, another rhythmically working a speed bag. All work in sync with the timer on the wall, which constantly bleats out signals for three minutes of work and one minute of rest.

I start jumping rope and my elementary school skills are quickly put to shame by a guy who could have taught Rocky a thing or two. Though I can't bust out any criss-cross or double-jump moves, I still get a good warm up after several rounds with the rope. We move to abs next and I get acquainted with a leather medicine ball wrapped in duct tape, a formidable opponent for my not-so-strong core. As I toss the ball back and forth with the jump-rope pro, Argiropoulos ambles over to work a heavy bag, jabbing at it to the beat of the music and lithely darting out of its reach as it swings back at him. "Hey, alright," he says with a twinkle in the corner of his eye he steadies the bag for another boxer to take a turn.

If there was a movie about Argiropoulos's life, it would follow the underdog-to-champion formula so closely that you might not believe he is a real person. As a boy of 5 in Greece, he contracts polio. The illness leaves him weak and the other children tease him and won't let him play soccer. He vows to become a boxer so that someday, he can beat them all up. Cue the montage of Argiropoulos growing up, exercising everyday to strengthen his mind and body. He runs up and down the mountains of his village. He fills a sack with sand and slings it over the almond tree in his backyard. This is his heavy bag. He bloodies his hands pummeling it. With his brother, a tailor, he sews his first pair of boxing gloves. They stuff them with cotton.

It pays off. He is strong. The kids want to play with him. He makes it to the Greek national boxing team. Later, he becomes its coach. He and his family move to the United States, the land of opportunity. He holds different jobs; electrician, gas-station owner. He opens a boxing gym at his house in a quiet neighborhood and all who train with him love him.

When I can barely catch the medicine ball, my abs seemingly on fire, it's time to put on the gloves. First come the wraps. Argiropoulos sits me down on a stool and shows me how to wrap my hands in long strips of cotton to stabilize my wrists and knuckles against the punches he's about to teach me to throw. You can buy wraps yourself at a sports store, or borrow a pair from Argiropolos if it's your first time. When my fists are wrapped and ready (and looking kind of badass, I have to admit), it's time to don the gloves. We stand in the "ring," which is marked with a shakily painted red line that bisects the uneven cement floor. When people actually spar, it's a matter of both curiosity and necessity that others in the gym move the edges to make room and watch. Argiropoulos holds up pads for me to swing at and we circle each other while he calls for different punches: jab, body shot, uppercut, hook. It is exhausting, and ridiculously fun.

After we dance in the ring, I officially join the ranks of people who love Argiropoulos, though he basically had me at "Hello." He shows me the heavy bag and new ways to rip my abs apart using elastic cords and an incline board. When I finish the two-hour workout, I feel like jelly. For the next three days, I'm sore in a thousand places. And I can't wait to go back for more.

Argiropoulos is there everyday except Sunday. So, give him a call at 617.390.5786.

Beginners welcome.