After Ali, where is next US boxing hero?

They have the most champions in Olympic boxing history and Muhammad Ali, Evander Holyfield, Oscar De la Hoya and Floyd Mayweather all won medals at past Games.

But the United States has not won men's Olympic gold since Andre Ward in 2004 and in london four years ago did not get one medal in the men's competition.

It might be stretching it to say that American amateur boxing is in crisis, but what's clear is that Team USA at the Rio Olympics is under pressure to bring that surprisingly long barren spell to an end when boxing starts on Saturday.

The naysayers back home are not positive, pointing out that American men qualified in only six of the 10 men's weight classes for Rio.

Worst of all, say the critics, is that there will be no US heavyweight on show in Rio.

For a country that once rolled out the likes of Ali, Holyfield, George Foreman and Joe Frazier at the Olympics it represents a dramatic decline.

Billy Walsh, a respected Irishman who has been a coach of the US boxing team since October last year, said on Wednesday: "The focus has really been on professional boxing in the US and amateur boxing was just a stepping stone towards that, they never really had a vision of being a boxing gold medallist.

"And the system itself when I got there... The system was just doing the same as they'd always done and were hoping for different results -- like they say, the first sign of madness."

A major problem, said Walsh, was that American amateurs were boxing like professionals -- typically meaning more rounds in a bout, giving fighters time to size up their opponent.

Olympic boxing contests are much shorter -- just three rounds for men.

"Eighty percent of guys that win the first round in amateur boxing win the contest," said Walsh, who is head coach of the US women but keeps an eye over the men too.

"We all start at 100 percent, we are under pressure, so there's that intensity that needed to change.

"We had to change the type of training, the engine, change the thought process."