FITNESS guru Darren Burgess is playing mind games at his new club, Adelaide.

And Burgess' desire to build mental toughness has been just as important as his fitness expertise, Crows ruckman Reilly O'Brien says.

Burgess has joined Adelaide from reigning premier Melbourne, where he oversaw a training regime that helped propel the Demons to their first AFL flag in 57 years.

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"He's really good at instilling belief in the group at how fit we are and how well we are going, which has been great," O'Brien said on Monday.

"He has played a few mind games with us ... it keeps us on our toes and keeps us guessing as to what we're going to do.

"That has certainly helped in our resilience and our mental toughness."

Burgess has deliberately kept Adelaide's players in the dark about their fitness program until almost the last minute.

"Things like not telling us how many reps we're doing, sending out sessions ... the night before so we're not knowing what we're doing, that sort of stuff," O'Brien said.

"A lot of it is between the ears really. Everyone around the League is really fit.

"But having that belief that you can outrun your opponent all day ... is really important.

"That mental side is just as important as the physical side and he has been able to do that."

O'Brien, who said the Crows were collectively the fittest they had been since he joined the club in the 2014 NAB AFL Rookie Draft, were following Burgess' blueprint which led to Melbourne's success last year.

"He has talked about Melbourne and their ability to work really hard but work really smart in their running as well in games," he said.

"We have talked about that and being really fit but then not necessarily having to use it, just by doing your work early and working together as a group.

"They (Melbourne) were obviously the best in the competition at doing that with their defence and we're looking to emulate that in the way we're playing."