Pan American Games gold medallist Kelsi Worrell continued a breakout season with a 100m butterfly victory at the US swimming championships, where former world record-holder Dana Vollmer finished fourth.

Worrell's triumph was no surprise, but nor was Vollmer's failure to make the podium just five months after giving birth to her son Arlen.

"It has been exciting and it has been fun," Vollmer said of motherhood and her effort to combine parenting with a newly launched bid to make the 2016 Olympic team.

"I've only been in the water for three months, I'll take a 58," the 2012 Olympic gold medallist said of the time of 58.94sec, which put her 1.67sec behind Worrell's winning 57.27.

The 21-year-old Worrell's time would have been good enough for bronze at the swimming world championships being contested this week in Kazan, Russia, opposite the US meet.

"I just wanted to keep getting better and keep working on the little things," added Worrell, who finished ahead of Felicia Lee and Christina Bechtel.

"It's weird, I've never really done two big meets back-to-back -- getting that mind-set that I can still swim fast."

She'll need that ability next year, when US swimmers will have to go through the pressure-packed Olympic trials just to get to the sport's biggest stage in Rio.

There were no US trials this year for the world championships, with the team selected late in 2014 including such marquee names as Katie Ledecky, Missy Franklin and Ryan Lochte.

But the biggest name in the sport is in San Antonio, with 18-time Olympic gold medallist Michael Phelps due to launch his campaign on Friday in the 200m butterfly.

Phelps qualified for Kazan, but was denied the trip as part of the sanctions for his drunk-driving arrest in September.

The 30-year-old superstar says he'll be hoping to put up times to rival those being produced in Kazan.

"Times are what I want to see here," said Phelps, who is also entered in the 100m fly, 200m individual medley and, in a departure from his usual routine, the 200m breaststroke.

"I have an idea of where I'd like to be," he said.

Vollmer, swimming just her second meet since her son's birth, said she had no expectations -- but the world championships have given her plenty of motivation nonetheless.

Sweden's Sarah Sjostrom broke Vollmer's 100m fly world record twice en route to winning the world title.

"Watching Sarah break my world record was hard," she said. "She'd been so close to it, I knew it was coming.

"But it also lit a fire," Vollmer added. "Instead of trying to fend her off now I get to chase her."

- Schmitt climbing back -

While Vollmer had set aside her swimming ambitions last season, and Phelps's comeback from a near two-year retirement was disrupted by concerns away from the pool, 2012 Olympic gold medallist Allison Schmitt says she can't worry about missing the worlds because she "flat out didn't make it" with her performances in 2014.

Schmitt, who this year revealed her strong Olympic showing in London -- where she won 200m freestyle gold and 400m free silver -- was followed by depression that she was slow to recognize and for which she was reluctant to seek help.

Her 4:09.51 in the 400m free was good enough for only sixth place in a race won by Lindsay Vrooman in 4:07.88.

But it was a big improvement on the times she was posting last year and she'll be hoping to follow up her Pan Am Games 200m free gold with a national title.

"I still feel confident in that event," she said of the 400m free. "Last summer I was swimming 4:17 so having two 4:09s is a step in the right direction."
Source: AFP