Actor Ben Foster says that preparing for the role of Lance Armstrong in a forthcoming movie has given him new-found respect for cyclists and, perhaps surprisingly, for the disgraced rider himself.

He will star as Armstrong in a forthcoming movie based on David Walsh’s book Seven Deadly Sins: My Pursuit of Lance Armstrong, directed by Stephen Frears.

Foster told entertainment website IGN that Armstrong was “one of the greatest athletes that's ever lived”, not just for his physical ability but for his “focus”.

Foster says he spent time among cyclists and on the bike in preparation for the role. He has certainly managed to look the part. A publicity still of Foster released last year has cropped up a couple of times mistakenly used in stories about Armstrong.

Of pro cyclists, Foster said: “Those guys suffer in a very specific way. It was really interesting to spend time in that community. I had no idea what it took to push the body that way.

“It's about being eight hours in the saddle. That's a lonely, ritualized — it's in circles. You're making circles. You're pushing past hunger. You're pushing past clarity of thought. It's a wild way to suffer. Your feet aren't going anywhere. You're going in circles up these impossible mountains.”

As for Armstrong himself, Foster seems to have developed an admiration for the rider who was stripped of seven Tour de France titles after the full extent of his and his team’s doping was uncovered.

He said: “In terms of his athletic ability, there aren't many like him. That's a combination of focus. It's as much will as being a physical body. He's one of the greatest athletes that's ever lived.”

The as-yet-untitled movie will co-star Chris O’Dowd as journalist David Walsh whose dogged pursuit of Armstrong contributed to his downfall.

But despite the revelations about doping, Foster thinks Armstrong was still something special. He said: “He came up in a time of doping, and it's my opinion, if you look at the statistics, you have to go down 17 or 18 guys for those seven years retroactively, at least, to find a clean rider.

“So it wasn't EPO [Erythropoietin] that made Lance the greatest cyclist. It was something far bigger. How he handled that ability, how he handled his will, that story's not over yet.”