Mal Whyte looks calm for a man who has spent the day quite literally bouncing off the walls. "No, I'm frazzled," he admits, as he clocks off from another day of rehearsals in the Matt Talbot Hall on Dublin's northside. "There aren't many actors my age that fall off ladders and do handsprings and that kind of rubbish." Cue one of Whyte's trademark chuckles. "And that's just in the warm-up!," writes Belinda McKeon.

The reason for all this bouncing and springing is Mouth, the new play written by John Dawson and Andy Crook for Articulate Anatomy, the high-voltage young Dublin company which made an impression at last year's Fringe Festival with its production of Peter Handke's My Foot, My Tutor. With an emphasis on the physicality of performance, the dynamism of the body - on, quite literally, the way the human anatomy speaks - the company requires boundless vitality and vigour of its actors.

And although he has a good quarter of a century over the rest of the cast - Anthony Morris, Mark D'Aughton, Jody O'Neill and Gillian McCarthy - Whyte is more than willing to come up with the goods. He's relatively fresh, after all, from one of the most exciting pieces of physical theatre to be seen on the Irish stage. No, that's not in his role as an English army officer in The Shaughraun at the Abbey, though the length of the run alone must have demanded some stamina, but in the Performance Corporation production of Tom Swift's The Butterfly Ranch, in which he played the callous and violent head of said ranch to chilling effect, energetically scaling the rails of a four-storey stage as he did so.

Most remarkable of all, however, was that this was a feat which took Whyte just one week to pull together; after the actor initially scheduled to play the rancher suffered a bad fall down the tiers of that same stage, Whyte found himself needing to get moving, and fast. "The original guy was six foot tall, curly-haired, late 20s," says Whyte with a grin. "So obviously, when they had to recast, they thought of me."

Though funny, it's true. Mouth is a cross between a thriller and a tragedy, skirting between the gritty and the surreal as it explores the realm of urban myth and conspiracy in the shadowy setting of an abandoned sweet factory; characters come together to create frightening stories, to deceive one another, to battle with their pasts and with their fear of the future. And these are not characters with great regard for one another; anger and paranoia runs high as language becomes a weapon, as bodies turn unpredictable, as bizarre interludes of starkly physical performance - dancing pizza deliveries, the unexpected activity of a hod of bricks - reflect the chaos at work in these gathered bodies and minds.

One of those gathered is Sam, the middle-aged widower who makes urban myths with his younger counterparts and bears the grief - and possibly the guilt - of his wife's sudden death. And, not unlike the people behind Performance Corporation, when Andy Crook, who will direct the production of Mouth, opening tonight at the Project Cube, needed an actor to fill these taxing shoes, he thought of Whyte.

Whyte will be the first to admit that the business of getting into a character's head in a primarily physical piece can be a taxing one. "Getting it out of the mouth, finding a character in there, it's hard, it's one of those that really has to be worked hard on," he says. Yet Sam has a history, a palpable past, which is something that some of the other characters lack. Does this help the actor's task? "Yes. I always fight for a back-story," he says. "I think that in all theatre, but certainly in a piece like this where it's precise, where it's movement-based, the text has to be just as precise, and your thought patterns have to be just as precise and know why you're doing something. And when you are stylising, you have to stylise from a very, very firm base . . . you've got to know what you're doing."

Reading the script, I confess to Whyte, I'm not exactly sure what it's doing - those unexpected sequences of strangeness, those manic happenings which come to disturb any semblance of flow, are difficult to integrate into an overall sense of the play, at least on the page. "Yes, it is dangerous ground," he agrees of the process of piecing together such a production, "because you don't know if it's going to work." But those odd, narrative-smashing forays will make sense, he promises, when the piece comes to stage as a whole. "My mantra is always 'why?'", he says. "And I put that to writers and directors. I'll work to justify something as a character, but they've got to do their work, too. Like anything, though, you don't expect people to understand what's going on straightaway. But hopefully over the show, it'll layer, it'll build up, so that those areas that aren't straight narrative will lead the audience into eventually understanding what's going on."

There have been times in his career when Whyte himself hasn't been sure exactly what's going on, or at least where things are going; coming to Ennistymon from London in the early 1970s as a musician who quickly found himself without a band, he plunged into a dizzy assortment of jobs, even of lifestyles, as he settled into his new home. "I did things that were . . . reasonably legal," he smiles, "farmed, ran a pub, ran a health food shop down in Clare, was a musician . . ."

Hold on. Health-food shop? In 1970s Clare? Wouldn't that have been something of an oddity?

"Yes," he beams, "it was the first one."

And trade? "It was hell."

Really? "Ah, it was grand. But I've always worked from the principle of doing something while it's fun. And that's usually for about a couple of years . . . then you get bored." It took him a while to get bored with his health food store, however; coming up to Dublin to buy fruit and vegetables, bringing back "exotic" fare such as chestnuts and pomegranates to display to his customers with pride, standing in the bleak cold in the winter of 1981 while his produce rotted under the frost and his chapped hands felt as if they were doing the same.

Okay, maybe not the last one. Rather, it's the experience on which Whyte found himself drawing as he sat in a trailer on the set of In the Name of the Father, waiting for hours to be called for the prison scene in which he played a part. Sharing his trailer with an actor who ranted and raved that he had been hanging about all morning with nothing to do, Whyte thought back to the misery of that winter.

"And I thought, this life isn't too bad," he smiles. Having come relatively late to acting, he appreciates its perks and privileges perhaps more than others do. On film sets, he revels in the hours of waiting so vociferously hated by actors; in the rehearsal room, he relishes the sense of fun which arises even in exploration of the most serious play. "I do really relish the enjoyment side of life," he says. "I like working hard; it's an ethic I've always had, but I love to enjoy myself, seriously enjoy myself. Serious enjoyment is great."

Such pleasures, he says, are part of the reason why he has never grown bored with acting, why he decided, having dabbled in amateur drama, to walk away from his shop in 1986 to move to Dublin and start professional training with Joe Dowling in the Gaiety School. "I said to the woman working in the shop with me, would you like to take on my job, I'll be away for nine weeks?" he remembers. "And she said yeah, ok. I closed the door in October 1986, and the next time I was in Clare was in April 1991."

The shop? "She moved on. It all took its course. It's a doctor's surgery now."

A part in the Gaiety production of Borstal Boy came soon after his enrolment in the course, and further stage work and film parts soon followed. Now, look at an Irish-made film from the past 15 years, and you're likely to see Whyte's face in there somewhere; among them are Michael Collins, Braveheart, TheLast of the High Kings, Some Mother's Son, Breakfast on Pluto and Man About Dog.

But it was the film scene of the 1980s and early 1990s which was the easier climate for a slightly older actor to work in, he suggests.

"I was in my mid 30s and there weren't the educational programmes then, the 20 to 40 young actors coming out every year. So I was a fresh face, and very usable." He laughs. "And films were alright then."

They're not alright now? "They're younger, Irish-centred films now so the parts aren't there. I've played my share of drunken old farts. And that's hard because they always want you to be a drunken old fart at half seven in the morning."

The early starts on film sets are not kind to someone who is required to do endless takes of pint-skulling, as Whyte has discovered on a number of occasions; a morning shoot of December Bride, in which he had to down a flat Guinness in three gulps - over and over - while his co-stars Donal McCann and Saskia Reeves looked on seems still raw in his memory.

"We finished about 10 or 11 in the morning and I was absolutely pie-eyed. I was doing a Rough Magic show that evening, and I remember walking around and around Temple Bar, trying to sober up."

So we should all reserve judgment of any drink-addled actors we might meet at ungodly hours of the morning, it would seem. Whyte, however, doesn't much care how his profession is perceived from the outside; it's what he does every day, and what he intends to keep doing for the rest of his days. "It's a microcosm of life, that's what I love about this business. That you live a life every few months, from beginning to end, you form relationships, you form friendships and enmities, you go through hell and heaven and high water together . . ." He smiles, and there's that gleeful laugh again. "And then maybe you never meet again. It's great."

Mouth opens tonight at Project Cube, Dublin and runs until May 7