The television commercial that depicts Michael Phelps digging into a gigantic sub sandwich has another meaning besides, “Swimming works up a serious appetite.

The ad also serves as a hint on not biting off more than you can chew, which illustrates his dilemma at the U.S. Olympic Swim Trials in Omaha, Neb.

The most decorated Olympian ever has entered seven races, which could qualify him for as many as 10 events, counting relays, in London. Phelps’ coach, Bob Bowman, expects him to pare the ambitious list to avoid spreading himself too thin, like a thimbleful of mayo for covering a foot-long.

Phelps, though approaching just birthday No. 27, maintains that this is his farewell Olympics. He will be tempted to choose quantity (amass as many medals as possible) at the risk of sacrificing quality (focus on golds and world records.)

In a sport whose athletes once had a short shelf life, the Trials is no longer out with the old, in with the new.

In fact, one of Phelps’ rivals, Jason Lezak, is 36. (Phelps’ chief adversary, the apparently tireless 28-year-old Ryan Lochte, has signed up for 11 events.)

The women’s side overflows with middle-agers, most notably Dara Torres, 45, gunning for her sixth Games. A blast from the past is Janet Evans, 41, attempting a quixotic comeback from retirement in Atlanta 16 years ago.

For inspirational stories, there is Eric Shanteau, recovered from testicular cancer that was diagnosed soon after qualifying for Beijing in ’08.

Also featured at America’s ultimate quadrennial pool party are veterans Natalie Coughlin, Brendan Hansen and Amanda Beard, along with newbies Missy Franklin, Nathan Adrian and Allison Schmitt.

But the main plot focuses on Phelps, the sandwich lover who must avoid getting into a pickle by biting off too many events.