Years before they began competing against each other for Olympic triathlon medals, the Yorkshire-born brothers were challenging each other to table tennis matches and tree climbing contests.
With a dazzling array of world titles to their names, including Alistair's gold and Jonny's bronze from London 2012, they are encouraging youngsters to follow in their footsteps and get active this half-term.
The sporty duo chatted to HELLO! Online about spurring one another along, mixed emotions on the podium and their suggestions for fun holiday activites.
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Have you always been competitive?
Alistair: We've been bitter rivals for as long as we can remember. We were competing whenever we played games in the garden or board games at home but now we're going head to head internationally at the Olympics.
Were you competitive at school?
Alistair: By the time we were at school we were so focused on sport that was our main competitive channel and we weren't too competitive with schoolwork, but when we were younger we were definitely competitive at everything, whether it was games or school or the garden.
Is your rivalry always positive or does it ever become negative?
Alistair: On the whole it was always positive. In the past there probably were times when we overstepped the line and fell out, but now it's always very productive.
Jonny, do you think Alistair will always beat you or do you see yourself coming through?
Yeah definitely, the gap is closing. I hope so anyway! But he keeps improving as well. All I can do is keep training as hard as I can.
When you beat each other is that a different feeling to beating someone who isn’t your brother?
Jonny: Yeah we treat each other slightly differently to other athletes. Firstly you try to beat everyone else on the world and then you have to beat each other.
Jonny, how does it feel to beat your brother?
Jonny: It's great but it's also tinged with disappointment if the other one hasn't done well so you always want the other to do well.
Do you have an advantage over your other opponents by training alongside together?
Alistair: Yeah absolutely, on lots of levels. Just being able to train with each other, having someone to motivate you to go out the door when the weather's bad, having someone to push you on in hard sessions when you feel tired and a bit rough, and in races too, is a massive advantage.
Is one of you more of a driving force than the other?
Alistair: I suppose it's equal and different on different days, one day one of us will take the lead, and in another the other will take the lead.
You don't live together anymore. How different are your houses?
Jonny: My house is really neat whereas Alistair's is a bit crazy – there are bikes and shoes everywhere.
Do your training styles differ in the same way?
Jonny: At certain times of year yeah, Alistair is often more chilled out in training. If it's raining he may cycle shorter and not get a full four hour ride in whereas I'm more strict with my training, I like to make sure I get the full four hours done and I won't cut corners even if it is raining outside.
How well do you take criticism from each other?
Jonny: I think we both take it quite well, especially from each other and especially when it’s constructive, definitely. I don't think Alistair has ever taken it too far because he knows when to stop.
How has life changed since the Olympics?
Jonny: It's a lot busier. We get recognised more and we have more things going on. But at the end of the day we go to the swimming or go for a run and life's still exactly the same and it hasn't changed at all.
Were you active as children?
Jonny: Very much so. Our parents always encouraged us to get outside and be active and that approach led led to a career in sport for us. We've teamed up with Warburton's Half & Half to get kids active and outside over half term. We've come up with 20 ideas which are on the Warburton's Half & Half Facebook page which are the kinds of things we did when we were younger – playing tug of war, making go-karts and tree houses – to inspire kids to have a go.
The Brownlee brothers are ambassadors for Warburtons Half & Half range helping parents smuggle goodness into family life. Visit their Scrapbook at www.facebook.com/warburtons for half-term inspiration