IRVINE, Calif. — Though he has swum four meets since his return to competition, Michael Phelps will gain a truer gauge of his form this week at U.S. Nationals.

The event, which begins Wednesday and runs through Sunday, will bring together the nation's best swimmers as they vie for spots in the 2015 FINA World Championships in Kazan, Russia. Analysts will have their eyes on Phelps, not only to see how he fares against world-class competition but to glean a hint of which events he hopes to swim at the 2016 Olympics in Rio de Janeiro.

This week, he's entered in the 100 butterfly, 100 freestyle, 100 backstroke and 200 individual medley.

"I think he'll be swimming most of the events you'll probably see him swim going forward," said Phelps' longtime coach, Bob Bowman. "It's a good test for him. He'll try to step it up another level."

Phelps acknowledged in pre-meet remarks Tuesday that his planned four-race schedule and the elite competition will make nationals the stiffest test of his comeback.

The Rodgers Forge native said he still harbors significant goals, though he was coy about them as usual.

"There are always things that I still want to do and still want to achieve, and that's part of the reason why I'm still here," Phelps said. "You're not going to get what it is."

Phelps hasn't publicly committed to aiming for a fifth Olympics. But the swimming world assumes that's his intention, given his decision to throw himself back into the daily drudgery of training after a 20-month retirement.

"This is an important summer for him because it does set up the next couple of years," said NBC swimming analyst and former Olympic gold medalist Rowdy Gaines.

'Pure speed'

The early stages of his comeback have revealed a Phelps who can still swim some of the fastest times in the world but who's less inclined to the rigorous event schedules that defined him in his prime.

He's training less than half as much, Bowman said. And Phelps has said he's enjoying himself more because he's setting his own schedule. He has spoken repeatedly of the fun he's having, a far cry from the run-up to the 2012 Olympics, when training became a chore.

Phelps grabbed the attention of swimming insiders with his most recent win in the 100-meter butterfly at the recent Bulldog Slam in Georgia. His time of 51.67 seconds might not seem like much, given that Phelps holds the world record at 49.82 seconds. But the time would've been good for fourth at the 2012 Olympics, and Phelps produced it at a relatively casual meet less than six moths after he returned to serious training.

"That's pretty jaw dropping," said Mel Stewart, a former Olympic gold medalist who analyzes the sport through his website, SwimSwam.com. "It's the kind of thing where, if swimming people are sitting around having a few beers, they'll look at that and say, 'Whoa!'"

The time prompted Stewart to wonder if Phelps, no longer burdened by the strength-sapping 400-meter IM, might be headed for his fastest swims ever in the shorter races. It's a potentially unsettling thought for rivals such as South African butterfly master Chad le Clos.

"We never saw just how fast he could be, the pure speed he could achieve," Stewart said of Phelps. "But now we're seeing it. He might still reach new heights."

The possibility is enhanced by the greater competition Phelps faces in daily training at the Meadowbrook Aquatic Center in Mount Washington. Bowman has assembled something of a dream team, with Olympic gold medalists Yannick Agnel, Allison Schmitt and Conor Dwyer joining rising stars such as Chase Kalisz.

"They all know they're going to be tested in practice every day," Bowman said. "They can't just slough it off."

'Small steppingstone'

By his own reckoning, Phelps has delivered a mixed bag of performances in his return to competition.