“THERE was boxing, skipping, running, sit ups and press ups and weight lifting,” intones Joshua Jenkins.

This somewhat puzzling answer follows an innocent enough query about rehearsals for The Curious Incident of the Dog in the Night-Time.

Some much-needed clarification later, it emerges that no wires have been crossed. Every day for an hour, Joshua, who plays our hero Christopher Boone, had to report for circuit training in gruelling boot camp-style rehearsals.

From the moment he waltzed in ready to deliver his lines in his sleekest RP, it became clear he would have to pull his weight, literally, to carry the production with the proverbial aplomb.

Set in Swindon, the National Theatre’s award-winning adaption of Mark Haddon’s novel follows Christopher, a 15-year-old with an exceptional gift for maths but ill-equipped to interpret everyday life. As the play opens his neighbour Mrs Shears’s dog is found dead, speared with a garden fork. Christopher, who is under suspicion, sets out to solve the mystery of Wellington’s murder, recording each fact.

His detective work, forbidden by his father, takes him on a frightening but eye-opening journey.

As the teenager struggles to articulate his thoughts, transporting the story to the stage meant turning a topsy-turvy world of muddled words and impressions into action. This physical take on the book sees Joshua leap into the air, launch into precisely choreographed routines, and tackle a gravity-defying ‘wall walking’ stunt.

“Christopher sees then world in a different way,” he explains. “He finds it overwhelming, his senses are bombarded constantly. In the play we express it through lighting, sound and movement. He does back flips, runs around the stage. It’s physically exhausting but it really guides you as to how he’s feeling.

“The whole company had to do circuit training for the first six weeks. We still do it now but only half an hour every morning. I was demanding at first. I had never had to do it for any other play or at any point in drama school. It definitely didn’t prepare me for that. But we were so exited. We all bought into the process.”

Although the story never fully sheds light on Christopher’s condition, it is “fair to assume” he is on the autistic spectrum, according to Joshua.

Ahead of rehearsals, the actor dusted off his dog-eared copy of the novel.

To convey Christopher’s bewilderment at the world around him, he also devoured articles and watched every documentary he could unearth on autism.

“Christopher is an amazing boy with a gift for maths and science but difficulties with normal interaction,” he adds without missing beat. “I had read the book quite a few times before and during the audition I read it again. Through rehearsals it was my bible. I was lucky enough to find out I had the role a few months before the job started so I was able to research the spectrum – it’s very broad - and Asperger’s specifically. I read as many books as I possibly could, watched documentaries and films. I met this boy on the autistic spectrum, parents and teacher. I just wanted to make sure I did it justice. But I didn’t want to fall into a type. Everybody on the spectrum is different; we are all different as human beings.”

Weight lifting aside, one of Joshua’s most daunting tasks was mastering the maths and equations in the script. Strolling around the stage tilted at a 90-degree angle was a quiet walk in the park compared to the prospect of memorising prime numbers.

“I learned the entire play in a month and it took me another month to learn the equations and the prime numbers,” he laughs. “I understand it now but it took a while. It’s safe to say that maths is not my strong suit.”

Ready to add side planks and mental maths as his new special skills on his growing CV, Joshua is intrigued to discover what the future holds. Yet, unlike Christopher he remains firmly grounded.

“There are a lot of Shakespeare roles I would like to play, like Hamlet. But you get what comes your way. Your career chooses you, not the other way around.”

The Curious Incident of the Dog at Night-Time will run at the Bristol Hippodrome from August 4 to 8. To book visit www.atgtickets.com/venues/bristol-hippodrome/ or call 0844 8713012.