<i>Spanish Heart of Fire</i>'s Tim Redmond and Rama Nicholas.

Spanish Heart of Fire's Tim Redmond and Rama Nicholas. Photo: Mark Gambino

STRANGE things happen when an ever-changing cast of actors improvises soap opera on stage for 52 hours straight. Delirious actors forget they're performing and walk off-stage mid-sentence for coffee. Some audience members are in sleeping bags and snore loudly. Exhausted critics nod off and wake with a start to find themselves surrounded by cast members singing a lullaby.

What began in Edmonton, Canada, in 1993 as a one-off fund-raiser for improvisational theatre company Die Nasty quickly grew into a weekly 53-hour cult hit that's still running nearly two decades later. Annual Die Nasty Soap-a-thons, each season with a different theme, continuing storylines, live music and recurring characters, have since spread to London, Liverpool and Cape Town.

Last year, original Edmonton cast member Patti Stiles, a Canadian actor, director and globetrotting impro teacher, brought Soap-a-thon to her adopted town of Melbourne. The first show featured a post-World War II theme and tested the endurance of 25 actors drawn from local impro companies, including Spontaneous Broadway, Impro Melbourne and Secret Impro Theatre.

This year's marathon, Spanish Heart of Fire, which starts at 6pm on November 30, features a cast of 45 from all over the country. The action - entirely ad libbed using prompts from the director - is punctuated by 15-minute breaks every couple of hours, allowing actors and audiences to take breaks as they please. Spanish Heart of Fire is set in 19th-century Spain, a theme chosen for its potential for passionate romance, revolutionary fervour, dodgy flamenco and the inspired anarchy in which impro specialises.

''In scripted theatre, you work really hard to … learn the story, and then you kind of forget it so you can live it,'' Stiles says. ''In improvisation, especially when you're doing storytelling … you're living the moment. So when someone turns to you and says, 'I love you', or 'I'm leaving you', you're . . in that space that you work so hard as an actor with a text to get to.''

Stiles served her theatrical apprenticeship under Theatresports creator Keith Johnstone at Calgary's Loose Moose Theatre. It was there she first saw the storytelling potential of impro, which in Australia is most commonly associated with comedy thanks to the popularity of celebrity Theatresports and television shows such as Thank God You're Here.

In Edmonton, Die Nasty brought together local actors with experienced improvisers, freeing both to cross genres endlessly using a dramatic technique with spontaneity at its core.

Die Nasty's productions mischievously add extreme fatigue to the mix, playing havoc with actors and audiences alike. Stiles was the first woman to perform the Edmonton show for 53 hours straight. She has seen actors perform to empty seats; and in states of exhaustion so acute, they forget where they are.

''When you're improvising, you're trying to connect to this spontaneous moment where there isn't any thought, where you're not pre-planning, you're just in this moment of impulse and allowing it,'' she says. ''Being awake for so long, you actually can't think, so everything becomes so real, everything becomes pure spontaneity and impulse, and it's really astounding as a performer to feel that. Now, sometimes we do get players who'll hallucinate [or] … lose words.''

Last year, one performer asked for food mid-scene. Another walked off to make coffee. ''Reality blurs,'' Stiles says. ''But it's amazing where the creativity goes, where the mind goes, and what happens in those moments.''

As director of Spanish Heart of Fire, it's Stiles' role to keep the storyline progressing even if performers and audience members start dropping like flies. ''When I'm directing, I don't want to tell the improviser the theme, I want to give them a seed or a starting point that's going to inspire them to find the story,'' she says. ''And if they're having a difficult time, or they're tired, or something's been missed, then I'll come in and help out.''

It's tougher for her than traditional performing. ''You need to keep all the threads of the story going, all the threads of each individual character going, and you're also looking for variety and pace, setting, mood, emotion, tempo, visual differences - you're really trying to craft that whole picture for the audience. [It's] really challenging.'' Especially at 5am.

Spanish Heart of Fire is at Brunswick's Broken Mirror Studios from 6pm on November 30 to 10pm on December 2. soapathon.com.au.