They are the AFL's depth collectors.

Collingwood coach Mick Malthouse is a disciple of the principle.

Hawthorn's Alastair Clarkson is a convert.

And Geelong, under first-year coach Chris Scott, are blooding youth to build their playing depth.

All with the goal of being paid back with a deep pool of 30 to 35 players ready to choose from in the finals.

So far it's working beautifully for all three.

Geelong, Collingwood and Hawthorn occupy the top three spots on the ladder.

As the AFL gets faster, the season more gruelling, and travel more wearying, the old maxim of "never change a winning team" appears to have become outdated.

"I just don't see how you can possibly get through a year, particularly in today's football, by minimising your (player) numbers," Malthouse says.

"We're very aware you have to have quality numbers at the end of the season ready to play football.

"I don't want to be in a position at the end of the year guessing about the form of players.

"The best idea is throw them in when they're in good form. When there's a position there, throw them in, give them a chance. That player then adds on to the list that you need."

Collingwood are the current masters of blooding youth at the right time - the latest example small forward Jarryd Blair whose 2010 mid-season debut ended in him playing in a grand final.

The Magpies have had three more young players - Luke Rounds, Alex Fasolo and Tom Young - force their way into calculations for the big Queen's Birthday clash with Melbourne on Monday.

Hawthorn coach Clarkson watched Collingwood's progress last season and has employed a similar strategy this season - with stunning success.

Midfielder Shane Savage and defender Matt Suckling have been outstanding inclusions - keeping some Hawthorn 2008 premiership players out of the side.

And the Hawks had fourth-gamer Luke Breust and young ruckman Max Bailey to thank for a last quarter fightback to beat Fremantle last weekend.

"Our side's changed by about eight players since six weeks ago," says Clarkson as his Hawks prepare to play Geelong on Saturday night at the MCG.

Geelong have just four players who have appeared in all 10 of their wins to start this season - Jimmy Bartel, Joel Corey, James Kelly and Travis Varcoe.

To go with their old guard, youngsters Mitch Duncan, Daniel Menzel, Taylor Hunt, Allen Christensen and Nathan Vardy have successfully added to the Cats' mix.

Malthouse says: "When you're relatively successful, and I'm talking about final four, you use 32 to 34 or 35 players."

Right now, the ultimate measure of success - the AFL ladder - backs up that thinking.

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