How sexy is too sexy? How far is too far?

For many of those who watched the MTV Video Music Awards, there was a palpable sense that former child star Miley Cyrus had already gone too far before she was even halfway through Sunday night's booty-grinding belt-out of her recent hit We Can't Stop.

Whether it was the flesh-toned latex two-piece, the creative and (ahem) self-indulgent use of that giant foam finger, or the de facto lap dance — delivered with an assist from crooner Robin Thicke's mid-section — many took a dim view of the former Disney girl's latest effort to break from the squeaky-clean image of her past.

"Disturbing" and "ugly" said a few choice Tweets.

Even The Hollywood Reporter — a publication better acquainted than most with the excesses and mercenary necessities of stardom — recoiled, in an editorial, from the "crass" performance, which its music editor opined was "reminiscent of a bad acid trip."

Still, veteran image watchers like Hollywood's Howard Bragman, vice-chairman of the management firm Reputation.com, says something like Sunday night's spectacle at the VMAs was a logical next step in killing off her former alter ego, Hannah Montana.

"These high-profile showcases are where you get to shake things up, get some attention, steal the show and send these kind of messages. And I think she did a journeyman's job of that," he says from L.A.

"Whether you agree with the message or not is a different issue," he adds. "But message received — loud and clear."

Cyrus's bump and grind recalled so many similar moments in the careers of other performers — many of them female, and Disney veterans — when the PG-rating of youth gave way to something a bit more NC-17.

For young women, that almost always means turning on the sex appeal, almost always to mixed reviews. Think of Britney Spears writhing with that snake to the tune of Slave 4 U in 2001, or her lip-lock with Madonna in 2003 — both other memorable VMA moments — or Christina Aguilera's eye-popping video for Dirty.

"We don't know what goes on behind the scenes at Disney, but all of these female stars seem to have such an urge to shed that good girl, teeny-bopper image," says Alanna Glicksman, a Toronto-based public relations consultant and entertainment blogger.

The transition is harder for women, she says, because sex "inevitably becomes part of the equation."

Glicksman also notes, with a laugh, that VMA honouree Justin Timberlake has pulled off multiple image re-dos by changing little apart from his hair and wardrobe — bleached when he was with 'N Sync, a buzz cut for going solo, dapper suits and hats these days for the more mature look.

"With him it's been a much simpler process. He had different bumps on the road, but he did not have to create a brand new image of himself every time," she says.

"It's harder for women to break the mould … because when you create an image, and are thrown in the spotlight as a good girl, you eventually want the world to see that you're not that little girl any more, that you're a woman."

Cyrus, 20, has been showing more skin for some time. She was at the centre of controversy in 2008 when it emerged she had, at age 15, posed not-quite topless for Vanity Fair.

Last month she appeared completely naked, but for some carefully placed lettering on a T-shirt in support of melanoma research, and there is plenty of hard partying on display in the racy video for We Can't Stop.

The trick to growing up in the spotlight, and going from child star to grown-up, is to control the message, in Bragman's view.

"Don't let it happen by accident," he says, citing Justin Bieber's many misadventures as a cautionary example.

"Miley Cyrus went out with the intention of giving a very provocative performance at a music venue and everybody's talking about it. Compare that with Justin Bieber and the last 40 times we've heard about him had nothing to do with his music."

"It's got to be well thought-out, well planned," says Bragman. "This [the VMAs]

was clearly not an accident. Whether it works or not — time will tell."

Glicksman agrees the VMA show was "very calculated" and that Cyrus needed to break from her Hannah Montana past. But did not need to take the low and more-travelled road.

"There is a way to be classy as you enter womanhood," she offers, citing the recent career of Selena Gomez, yet another pop princess now mid-segue into adulthood, as a better role model.

"Miley, I think, is taking it to new extremes … I don't necessarily think she's portraying an appropriate image, especially given her existing fan base. She's not a role model for young girls and parents won't want kids looking up to her."