He said: “I keep myself very fit. I played soccer all my life – don’t so much anymore, because I had a knee replacement. And I’ve always had a trainer – same guy for 38 years.
“I have an indoor pool, massive gym, golf course, everything. We do a lot of underwater training, where the trainer throws a brick into the pool and I have to dive in, push the brick to the end of the pool, and come up.
“Frank Sinatra once said to me: ‘Rod, the secret to being a great singer is having powerful lungs. Do lots of underwater swimming, where you hold your breath.’”
The Scottish singer said he hates it when reviews of his shows imply he doesn’t have the stamina to make it through a full concert because he needs a “rest”.
He fumed: “Critics say, ‘Rod was great, but he had to take a rest.’ Drives me mad!
“When I do concerts, I change costumes, mainly because I like to show off, but also because I sweat a lot. I’m not resting. Taylor Swift goes offstage about a dozen times, but they don’t say that about her because she’s young.”
To mark his 80th birthday in January, Stewart and his whole family enjoyed a celebration on a yacht, and his wife Penny Lancaster secretly arranged for everyone on board to dress up as him.
Asked how he had celebrated hitting the milestone, he said: “We hired a massive yacht. Cost me an absolute fortune. I don’t mind, you’re only 80 once.
“I’ve got eight kids and five grandchildren, plus various boyfriends and husbands, so there were 15 of us.
“We had three chefs. The boat was so big that I didn’t even see some of it. We dressed up every night, with a different theme.
“One night, they all dressed up as Rod Stewart and didn’t tell me. My dear wife brought wigs for everybody and some of my old outfits. It was a wonderful time.”
