Stewart, who is married to model Penny Lancaster, 52, says that he's even been swimming with weighted bricks ahead of his UK tour in November and December.
Stewart told the Daily Mirror newspaper: "It was 'SAS' style. Nothing stops me from doing that. It was in a 20-metre indoor pool, where we do some SAS training by swimming with weighted bricks under water, and all sorts of joviality."
"Sometimes when you exercise you think, 'f*** I can't be bothered to exercise this morning.' But then you push yourself, it's just so uplifting for your mind and body. If I go 10 days without working out, I go in the dumps."
As per 'Female First UK', the rock'n roll singer who is best known for classics such as 'Hot Legs', 'Young Turks', 'I Don't Want To Talk About It' and 'Da Ya Think I'm Sexy?' lives in Harlow, Essex, south-east England.
SAS stands for Special Air Service who are the special forces of the British Army.