She has in the past been rather scornful of what she had always considered the rather desperate attempts by some of her fellow actors to battle the passage of time by daily 4am gym sessions. Now Helen Mirren has revealed that she herself partakes in gym workouts - "occasionally" as she says in an interview in the Sunday Times on 27th March. At her age (71, if you're interested) she says "it's necessary". No evangelism, no fuss, just an understated acceptance that working on her body is an essential part of keeping herself fully functioning and in good shape to continue the work she loves.
So it's as simple as that, you have to do it. And if The Queen says it, it must be true!