Erin McNaught just revealed the most surprising celebrity exercise tip we've heard.

Celebrities are known for keeping fit in unusual ways. Britney Spears walks backwards on the treadmill, for instance, while Zooey Deschanel hula-hoops.

But Erin McNaught has just shared what is perhaps the most surprising — and adorable — fitness tip we’ve heard in a long while.

RELATED: The reality of doing exercise when you have kids.

The Aussie model told the website Wonderful Mama she’s found a new way to weight train, and it doesn’t involve any fancy equipment. In fact, she doesn’t even need to leave the house.

“[A] great way to get back into shape is to use your baby as your weights!” McNaught says, referring to her five-month-old son Evander, who she calls Van.

“Run around the house holding him as an aeroplane – Van laughs his head off when I do this. Your baby will love the bonding time and your arms will burn!” (Post continues after gallery.)

Anyone who’s ever lifted a baby will see the logic in this. It mightn’t feel like a lot of effort at first, but after a while your muscles will protest. McNaught says there are a few different ways she incorporates Evander into her workout routine.

RELATED: 10 easy exercise tips for busy mums

“You can also do squats while holding him or lay him on the floor and do push-ups over the top of him, giving him a kiss or blowing a raspberry on his tummy with each time you go down. Incidental exercise all adds up!” the former Miss Universe Australia — who is married to musician Elliot ‘Example’ Gleave — says.

Who needs a kettle-bell or dumbbells when you've got a small child within reaching distance? The added benefit being, of course, that babies are also much better company than inanimate gym equipment. Cuter, too.

Evidently, McNaught's new fitness buddy has really been holding up his end of the deal. On Instagram, the 33-year-old shared a photo of herself doing chin-ups at the gym — an achievement she credits in part to little Evander.

RELATED: Everything you need to know about exercising after a C-section.

"After I had Van I realised I couldn't even do a single chin-up so I made it my mission to get strong again," she wrote.

"I can now proudly say I can do eight in a row! I started with assisted chins and lat pull-downs before trying to do one, then two, then three, etc, until I reached eight! This week I'm going to try and do three sets of four (three by four) to ensure I keep getting stronger." (Post continues after video.)

When an Instagram follower and fellow mum asked McNaught about regaining fitness after giving birth, she responded with some sound advice for getting back into the swing of things without overdoing it.

"Running was actually one of the last things for me to resume after having Van - your pelvic floor takes a while to regain its pre-preg strength so I started off with walking, slowly building up duration and intensity. Then I ran for 10 to 20 seconds every few minutes - do this as you feel comfortable," McNaught wrote.

RELATED: The 15 biggest fitness trends for 2015

"Only start exercising once you've had the ok from your doc and above all, listen to your body as you know it best! In the meantime, gentle squats, lunges and push-ups (done on knees initially, until your core starts getting stronger) will help you regain/maintain strength and muscle tone. Good luck!"

In her interview with Wonderful Mama, McNaught elaborated on her favourite ways to stay fit — but acknowledged that having a young baby can complicate things. When Evander is at home with dad, McNaught takes the opportunity to hit the gym.

RELATED: How to use the weights section at the gym.

"I do a lot of body weight resistance – burpees, tuck jumps, mountain climbers, planks, lunges, jump squats, etc," she explains.

"I also love kettlebell work and my absolute favourite is boxing but with my husband looking after Van, it’s sometimes hard to find someone to box with! I also try to go for an eight to 10km run once a week. It clears my head and gives me valuable ‘me’ time."

How do you stay fit?