Ross Lyon's pre-season demand for Clancee Pearce to get rid of his "fat arse" has given a revealing insight into the brutal fitness focus the Fremantle coach put on his players after taking the reins.

Just 23 days after being elevated from the rookie list, where he has toiled for the past three years, Pearce played a telling role for a third straight game in Fremantle's pulsating 13-point win over St Kilda last Friday night.

His emergence is both a testament to his gritty resolve to lose weight and get fitter in the pre-season and Lyon's savvy patience in giving him the chance to stay at the club after he was de-listed.

"From the outside, he played well against the Saints and was a booming kick and I thought he had some attributes," Lyon said on Melbourne radio station SEN.

"When I walked in the door he was being de-listed