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"Tick-tock, tick-tock," Madonna’s backup singers sang as video screens and subwoofers blasted to life at the Izod Center. Time obsesses Madonna on her Sticky and Sweet Tour, which made its first American stop on Saturday.

Time means beat and rhythm, and it means the pop history encapsulated in the hits Madonna has been making since 1982. It also means the aging that she defies with workouts, image makeovers and what looks like plastic surgery. At 50, Madonna can no longer be seen as a clubland ingénue, a Hollywood glamour queen, an iconoclast rejecting a Roman Catholic upbringing or a kinky provocateur, and she won’t be any kind of dowager yet. Time has brought out her core: careerist ambition and a combative tenacity.

Has there ever been a colder pop sex symbol? For all the invitations in her lyrics, Madonna has always projected more calculation and industriousness than affection. She works; her audience looks and pays, becoming another conquest.

"I can keep on going through the night," she insisted in "Heartbeat," from her latest album, "Hard Candy" (Warner Brothers), which provided nearly half the concert’s songs. That was the point: There she was, 50 be damned, strutting, pushing her dancers around, even doing double-Dutch jump-rope steps without a tangle.

Madonna built her stardom on her assets — her ear for hooks and beats, her looks, a predictive fashion sense and an instinct for pushing cultural hot buttons — and the Sticky and Sweet show insists, even demands, that they still have their effect.

She pumps up the volume, piles on the beat and mixes the unstoppable and the baffling, the thrilling and the ridiculous. The set had four thematic sections: the present-day dance floor, the old school, the big wide world, and political and spiritual aspirations (via the dance floor). For thumping electro songs from "Hard Candy" she had the album’s hip-hop guests — Kanye West, and Pharrell Williams — performing on towering video screens, sharing the proudly mercantile sentiments of songs like "Candy Shop."

The old-school section, with a backdrop of animated characters invented by the artist Keith Haring, riffled through original elements of hip-hop culture — break dancing, D.J. scratching, double Dutch and graffiti — along with (inexplicably) some pole dancing. Since punk and hip-hop were contemporaries, Madonna also picked up an electric guitar for an enthusiastic punk-pop version of "Borderline." Her moves were aerobic, not erotic; in one song, other dancers spotted her as if they were personal trainers.