The latest installment is taking place at the same venue that staged last week's Pan American Championships here - with nearly three times as many athletes.

Staff and volunteers went to work as soon as the Pan Ams finished, transforming the arena at Miccosukee Resort by taking out seats to make room for three platforms rather than one.

There are 782 lifters aged from 13 to 74 competing, from 8am until 10pm, over three days.

With coaches and family, the total number of people at the event is about 1,100.

By the time the December finals are finished, the four-part series - sponsored by Nike and Rogue Fitness - will have featured entry lists totalling more than 3,000.

The field for part three of the series, in Grand Rapids, Michigan, in September is on target to break the 1,000 barrier.

"It's record-breaking numbers anywhere in the world - and that's with qualifying standards," said Phil Andrews, chief executive of USA Weightlifting, whose number of registered athletes has more than trebled to 27,000 in recent years.

"If you took these numbers across to other sports it's like a taekwondo competition with 20 mats, fencing on 60 pistes, or table tennis on 150 tables."

Sarah Robles and Colin Burns, both Pan American gold medallists last week, are among the national team members who have competed in the American Open this year.

"Anyone, provided they meet qualifying standards, can compete against Olympians, which is a great experience for them," said Andrews, who pitched in yesterday to do the announcing on one of the three platforms.

The numbers are up, too, in local and regional competitions from California across to New York.

"We have 1,300 lifters in New York, double what it was a few years ago," said Chris Smith, an official at the Metropolitan Weightlifting Association in Miami.

"In the 1980s and 1990s we would have 30 or 40 people competing at our events, and the last two have had more than 100.

"It exploded around 2013, '14, '15 when CrossFit really took off."

The popularity of competitive fitness in CrossFit has fuelled the weightlifting boom, because so many people try it for the first time.

None of it could happen without an army of volunteers - there are 60 to 70 technical officials in Miami, plus loaders, security staff, announcers and volunteer coaches, all working long hours for the love of it.

"The commitment of volunteers is the only way we can grow the sport," said Andrews.