RIO DE JANEIRO, Brazil — Armies of shirtless men pushed opulent floats toward Rio’s samba stadium yesterday for the centrepiece of Brazil’s carnival celebrations, a hard-fought samba dance competition.The parades last all night Sunday and Monday, featuring women wearing impossibly high heels and glittering body paint shaking their stuff alongside bare-chested men. Thousands of elaborately costumed dancers and hundreds of drummers escort the floats, keeping up an ear-splitting rhythm.

But it’s much more than pure spectacle. The groups spend upward of a million dollars to mount 80-minute-long spectacles in the Sambadrome — a 60,000-seat venue built exclusively for the parades — featuring as many 4,500 dancers, all in an attempt to impress a panel of judges made up of folklorists, musicologists and carnival scholars.

The 13 competing dance groups come from the city’s shantytowns, and their showdown is a welcome distraction from the gunfights between drug traffickers, militias and police that have left at least 15 dead over the past week alone in the hills around downtown Rio. Adoring fans follow the live broadcasts with a passion usually reserved for the World Cup.

This year organisers have change the rules to wrap up the parade at an earlier hour. In the past, the Samba parade dragged on well past dawn, ending as late as 9.30 a.m., with revellers often struggling under the weight of heavy costumes under the punishing tropical sun.

The schools are judged in 10 different categories including music, the quality of their dancing and floats, their parade theme, and crowd reaction. A less than perfect score can dash a school’s chances of victory.

The featured dancers — especially the female flag bearers and their male counterparts — practice all year to perfect their steps, which are actually closer to minuet than samba.

“Being a flag bearer is almost like being a ballet dancer, it’s not just samba, not everyone can do it. For me it’s a way of life,” said Selma Sorriso, flag bearer for the Beija Flor carnival group.

Being relegated to the second division — which gets much less television exposure — means losing hundreds of thousands of dollars in sponsorships.