• The unusual installation is part of a career retrospective of Serbian performance artist Marina Abramović.
• The exhibition has otherwise received mixed reviews from critics - the Guardian called it "vital" but the Times said it was "remorseless".
Visitors to a new Royal Academy exhibition must squeeze between two nude models to enter it.
The unusual installation is part of a career retrospective of Serbian performance artist Marina Abramović.
There is a separate entrance for those who are uncomfortable squeezing through the nude performers.
The exhibition has otherwise received mixed reviews from critics - the Guardian called it "vital" but the Times said it was "remorseless".
Entering between the two naked performers forces those with tickets into a "confrontation between nakedness, and the gender, the sexuality, the desire", the Royal Academy's head of exhibitions Andrea Tarsia has said.
The unusual piece was first staged in 1977 by Abramović and her then German partner, Ulay. The pair stood close together in a doorway, compelling visitors to pass between them.
The Telegraph's critic Alastair Sooke said he was "too preoccupied with not stamping on their toes" to be able to sense whether there was a frisson as he passed during the new installation in London.
"You don't have to go through the naked gates. There's a bypass, but it's cheating," added the Times' Laura Freeman. "I squeezed through, sucking in my stomach, trying not to tread on anyone's toes or brush against anything."
The retrospective takes in Abramović's half-century career. She is the first female artist to have a solo exhibition in the Royal Academy's principal galleries in its 255-year history.
The Evening Standard's Ben Luke awarded it four stars, writing: "For once, this is not hype. I can't imagine a better display, especially given that much of it exists as documentation of performances.
"The staging of this material on film and in photographs is exemplary, and it's aided by four live pieces from different moments in Abramović's career, reperformed by Marina-approved artists."
He added: "I struggled to picture how the vast galleries of the RA could be filled by an artist whose practice has inevitably been largely ephemeral, when they have swallowed and diminished more conventional artists. But there is no sense of padding. The pacing is great: it's spare where it needs to be, busy and noisy at the right moments."
But there was less enthusiasm from the Telegraph's Sooke. In a two star review, he said: "The issue is the work. Is there a more egregious case of an artist, over the decades, losing their way?
"Those performances from the 1970s and 80s - many of them collaborations with her then-partner, the German artist Ulay - still seem radical and courageous, with something urgent to say about, for instance, the complex relations between men and women, or the gendered roles that society forces us to play."
Sooke added: "Over time, though, as Abramović became less concerned with corporeal endurance, and more interested in trialling her mind, she started to believe the hype.
"The result? Narcissistic art, devoid of risk, with none of the rigorous, visceral, blood-spattered toughness of old. Ritualised cleansing, in the form of scrubbing bones, is one of her motifs - but, ultimately, Abramović has ended up sanitising herself."
Freeman of the Times was similarly lukewarm, awarding two stars and saying there were "two principal problems with this stylishly presented but unsatisfactory retrospective".
"First: you thought performance art was bad? Old videos of past performance art are worse. Second: Abramović, who has made her career and artistic reputation teasing, testing and breaching the limits of her own endurance, may be hard as nails, but she is 76 and an honorary Royal Academician, so her part is played by acolytes.
"I'd like to say they were as fearless as the original but the three young women I saw performing Imponderabilia, Nude with Skeleton and Luminosity seemed self-conscious and under strain. Seventies body hair is out, bikini waxes are in. That alone would suggest anxiety more than abandon."
But the Guardian's Adrian Searle was more positive, calling Abramović's show "terrifying and vital" in his four-star review.
"We see her knitting, smoking, holding a candle and walking with infinite slowness, carrying a bowl of milk," he said. "Here she is lying naked under a skeleton in a kind of video sarcophagus, on top of which a naked live performer repeats the pose.
"Other performers re-enact early works as we go from room to room. There are so many Marinas here, but only one Abramović, in all her multiple guises.
Abramović is "redoubtable, indefatigable, brave and extreme", he wrote.
"I speak as one who has been moved by her endurance and spirit and laughed at her mordant wit, and also as one who has enjoyed a couple of her workshops and run away from another," he added. "But who cares about the mumbo-jumbo when the best of her art is so strong?"