A US father and fitness expert has written a book telling other dads how to turn their babies into effective gym equipment.
Joshua Levitt says he came up with the idea for Baby Barbells after realising there was less time to hit the gym following the birth of his own children.
Mr Levitt, 36, a father of three, told The Guardian that it all started when his oldest daughter, Sircia, now eight, was a baby.
"I came home from a long working day and my wife just handed me the cranky baby and said it was my turn," he explained.
When cuddles and soothing words had no effect, he lay down on his back with daughter Sircia on his chest and began lifting her up and down.
"I was saying, 'baby up, baby down' and Sircia started giggling away. At the same time I started to feel the burn in my triceps. I realised I was on to something. This was multi-tasking," he said.
From there he developed an entire exercise routine, including moves called baby bench press, lullaby lunges and peek-a-boo pop-ups.
"I knew I wouldn't be winning any body-building contests this way, but I realised at that point that I was in the worst shape of my life. I had to do something," he added.
Sircia was followed by Callie, seven, and son Zaiah, four, all of whom continue to treat their father as a "human jungle gym".
Mr Levitt added: "As they get bigger and they can balance better, they can do different stunts and I in turn get stronger and fitter."