By Martyn Herman

LONDON (Reuters) - Former world BMX champion Liam Phillips sums up the brutal nature of his adrenaline-fuelled sport succinctly.

"There are not really any rules on physicality," the 27-year-old Briton, preparing for a third Olympic Games, says.

"You can't take your feet off the pedals and kick somebody but after that pretty much anything can happen."

For sheer intensity, thrills and spills, the BMX races on the rollercoaster-like Deodoro course at next month's Rio Olympics will have no equal.

When the starting gate goes down, riders will plunge eight meters down, pumping their pedals for rapid acceleration, then hanging on over the lumps and bumps.

Medal hopes can vanish in the blink of an eye -- as Phillips knows all to well after crashing in the final in London four years ago having recovered from a broken collarbone just in time to take his place on the team.

While BMX racing can look chaotic, it is an extremely technical sport and the power produced by the world's top riders is similar to that put down by track sprinters like Chris Hoy, Britain's most successful Olympian.

Phillips said the start is crucial.

"You are basically eight meters up, lined up with seven other guys and then you go," Phillips told Reuters.

"It's a bit like a 100m sprint but there are no lanes. It's a fight to get to the first corner, then after that you can move to the best line and dictate a little bit.

"After that it's about staying as smooth as possible.

"If you make a bad start, and I'm talking fractions of seconds out, you're in trouble. Usain Bolt wouldn't last long in BMX racing because he's not the best starter -- he would be cut off straight away."


While Bolt has a lane to himself, territory is fiercely fought over in a BMX race.

"Someone can come underneath you in a corner, an elbow can catch you, suddenly you're on the floor," Phillips said.

"Nine times out of 10 it stays on the track. There is a mutual respect, but I'll make myself heard when I need to."

Phillips won the world championships in 2013 in New Zealand and last year became the first man to win back-to-back UCI BMX Supercross World Cup titles.

This year has been a little disappointing, although everything has been focused on Rio where he will be one of six riders he expects to be contesting for gold.

"It's been a little hit and miss to be honest," Phillips, whose parents Pete and Sharon used to drive their BMX-mad son to junior events all over Europe in a converted truck, said.

"It's a difficult balancing act. The injury risk is quite high in BMX. I didn't need to win any races because my Olympic spot was guaranteed. I was racing at 99 percent rather than 100 percent and it showed."

Phillips, boyfriend of track cyclist Jess Varnish, whose omission from the British team ignited a controversy that led to team chief Shane Sutton quitting, said the Deodoro track in Rio would be technically challenging, but hopefully safe.

"It was unrideable when we first went out there, some of the jumps were dangerous. It was insane," he said. "But at least it's possible to ride a lap now. Before that was impossible."

Whatever the outcome in Rio, Phillips said he would soak up the atmosphere.

"When I was a kid I would never have believed one day I would be riding my BMX bike in the Olympics," he said. "So I'm just grateful I will be riding in front of huge audiences.

"I just love racing."

Varnish, who was dropped from the British team after failing to qualify for the team sprint for Rio, will not be in Brazil.

Phillips describes her treatment as a "massive injustice" and said he was looking forward to the findings of an independent review into British Cycling.

"As a member of the team I'm welcoming the review because changes need to be made," he said. "There are still people working there that aren't in it for the right reasons."

(Editing by Peter Rutherford)