MANSFIELD - Nick Hexum, frontman of the band 311, works as hard as any “Glee’’ actor or “American Idol’’ onstage, what with all the calisthenics, jumping up and down, raising his arms like he’s in a Broadway finale, and exhorting his fans to do the same (well, maybe not the calisthenics part - beers and egos, foolhardy bedfellows such as they are, would undoubtedly become quick casualties).

And yet, at the latest installment of his band’s annual “Unity Tour,’’ before a near-packed house Saturday night at the Comcast Center, the clean-cut Hexum - toned, tanned, and clad in a Stanley Kowalski-style T-shirt designed to showcase those flexed triceps - appeared to not even break a sweat. He cavorted to the head-bobbing ’90s rap-rock of the opener, “Beautiful Disaster,’’ and the irritating singsong-y melody of “Come Original,’’ barely salvaged by 311 DJ-singer S.A. Martinez’s fierce, tightly wound rap.

Overall, Hexum’s showbizzy demeanor seemed at stress-free odds with heavier fare such as 311’s dense rap-metal smash, “Down,’’ and the gonzo hedonistic spirit the Nebraska band has spent two decades cultivating (its name reportedly comes from the Omaha Police Department’s code for “indecent exposure’’). Actually, 311’s best song Saturday, “Stealing Happy Hours,’’ was also an aberration: a graceful ballad buoyed by a silk-smooth groove and a soaring, lyrical solo by lead guitarist Tim Mahoney.

At 100 minutes and 22 songs, this was a mid-career marathon, executed with the broad brush strokes and boilerplate blare of ’90s alt-rock, not the dash or dizzy smear of spontaneity. And with stamina-testing solos by bassist P-Nut and drummer Chad Sexton - which ended with the whole band banging away, like a Blue Man Group audition, on a phalanx of percussion wheeled to the front of the stage - the show proved as long as 311’s latest album, “Universal Pulse,’’ is short (under 30 minutes). Unfortunately, a couple of the newbies, “Wild Nights,’’ and “Weightless,’’ proved just as anemic, fitted with a skimpy repeat-chorus formula and ultimately, indecently exposed.

Van Halen did it - several times. Journey did it. Alice in Chains did it. Even the Doors tried to do it. But a band replacing its lead singer and signature face and voice is tricky business, usually met with varying degrees of skepticism, outrage, and mixed results (at best). So the band billing itself as Sublime With Rome - featuring bassist Eric Wilson and drummer Bud Gaugh, both surviving members of the ’90s ska-punk band Sublime (whose frontman Bradley Nowell died of a heroin overdose in 1996) - has drawn both scorn and support.

Now fronted by singer-guitarist Rome Ramirez (but prohibited from using the old moniker because of a lawsuit brought by Nowell’s estate), the new incarnation has a new album, “Yours Truly,’’ that trades heavily on its old sound. During its spirited hourlong opening set Saturday, the crew dosed fans with old Sublime faves such as “Santeria’’ and “What I Got,’’ but also delivered heavier dub and reggae-flavored new songs like “Murdera’’ and “Take It or Leave It.’’ At one point, Ramirez sang a snippet of “Rehab,’’ the hit by British soul-pop singer Amy Winehouse, who had been found dead earlier in the day in London of a suspected drug overdose. She was 27. Fifteen years earlier, Nowell had been 28.

Jonathan Perry can be reached at roughgems@comcast.net.

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