When junior staff in the group, mostly female, ignored the rape comment, a further message, purportedly sent from Mr Brain's account, said: "No-one up for this then?"
SICK GIBE
Concerned staff reported the messages to the university's HR department in January but were left unaware of any action being taken.
A source at the gym said: "It's like they're trying to brush it under the rug.
"People are feeling let down.
"The university is loud and proud about its zero tolerance policies, but a lot of people want action on this — they feel abandoned."
Staff are now struggling in a "toxic" environment with no faith in protocols if they report misogynistic or inappropriate behaviour, the Edinburgh Evening News reports.
LET DOWN
The gym source added: "Staff were told there'd be an investigation in January and have heard no more.
"There are offhand sexist remarks, particularly working in the fitness industry, that are leftover attitudes that haven't made their way out yet.
"One senior manager apparently told female members of staff they must wear tight leggings because 'it looks more professional'."
A University of Edinburgh spokesperson said: "We take incidents such as this very seriously — the use of such language is abhorrent and has no place in this university."