Certain tensions in the jazz world were clearly evident at the 10th annual Yokohama Jazz Promenade on May 25th and 26th. The performers split into two camps: those focusing on instrumental virtuosity and those avoiding the staple four-beat ching-chick-a-ching-chick-a-ching rhythm. The plasticity of rhythm become the common thread of the weekend -- and jazz was pulled in all different directions.

Dutch drummer Han Bennink gave the most spectacular display. Arriving alone on stage in shorts, bandanna and socks, he proceeded to give a demonstration of the "drummability" of just about everything. He used his feet, elbows, hands (open and fisted) and knees to play the stage, the floor, a trash can, a towel, his thighs and the stairs leading up to the high, back seats. Just when I said to myself, "He'll be playing his teeth next," he did just that. Teeth are surprisingly loud, it turns out, resounding throughout the packed hall with only the amplifying help of the body's resonance chamber.

Other groups also ripped up the four-beat. The speed-freak, Middle Eastern sound of Cicala-Mvta was dizzyingly fun. Their eclectic combination of clarinet, electric violin, sax, cello, electric guitar, tuba and two full drum sets fused into sonic density, but there was still room for duck calls, electric samples, feedback loops and the occasional vocal (the violinist sang his apology for showing up late). Their swirling melodies and throbbing rhythms sounded more like the soundtrack to a whirling dervish festival than any New World jazz form.

Singers were no less interested in switching rhythms away from the lock-grip of traditional jazz vocal settings. Yukari Miyazono on "throat" and Kaori Osawa on piano offered a minimalist, reflective set that sketched tones, beats and harmonies without filling in too much detail. This impressionistic flow of often wordless vocals flowed unpredictably, with Osawa responding in support. Miyazono's voice moved in circular patterns of trinkling harmonics and deep guttural moans that were intriguing in their remoteness from mainstream jazz vocals.

Well-known singer Shun Sakai had no drummer at all. Her backing band -- guitarist, accordionist and flute/sax player -- let time drift in a loose, desultory fashion that soothed the standing-room-only crowd. A constant rhythm would have been disturbing. On an eclectic selection of tunes from pop (Sting), punk-folk (The Pogues), bossa nova and jazz standards, Shun followed her own internal rhythms. On each song, rather than fit herself into the beat, she made it conform to the shape of her own expression.

Even Takehiro Honda's Pure, a large, ostensibly blues-funk jazz collective, playfully experimented in the search for more flavor than a straight tempo could yield. The right half of the stage was taken up with three percussionists, with another, the amazing Grace, on a huge drum set smack in the center. Even when the group sank joyously into Grace's groove, they still stopped and started mid-song, as if the beat was just a toy to pull apart and put back together.

It wasn't all experimentation, but even those performers working in a more traditional mode used speed and dexterity to push the limits of time. Pianist Paul Tobey, part of the invited contingent of Canadian jazz bands, whipped through a virtuoso demonstration of fast melodic invention. With Oscar Peterson-like flourish, his self-assured trio shot through standards and a few originals such as the 7/4 time "Ko-garu" with accomplished control.

Similarly, for the bop technique of Hideo Oyama, the rhythm was as fast as the metronome could be set. His tone avoided the romantic swing of many sax players, but in any event he went too fast to bother with vibrato. His versions of "I Remember Bird" and "Night and Day" were crisp, clear and right to the point. He focused on fast-fingered technique, but was never stuck there, eventually pulling all his quickly hit notes into a pointillist whole.

A similar attention to instrumental mastery at high speed could be found in the guitar work of Takaaki Miyanoue. With a clear Wes Montgomery influence, Miyanoue has polished the very difficult technique of chord soloing. His quick-flowing three- and four-string chords were strikingly fast. The rhythm was standard, but his sheer skill gave it fresh energy.

Another crowd favorite was Shibusa Shirazu. Their take on rhythm was more organic. They seemed to find their collective beat by simply jumping into it, with an oompah here and a Jimi Hendrix blues there for direction. The crowd, though dancing and clapping along, mostly kept their eyes on the scantily clad, white-painted dancers, who moved to an otherworldly drummer of their own, crawling up and down the massive stone walls of the massive outdoor boat dock converted to a stage.

The most interesting group of the weekend, however, turned out to be the youngest. Jazzy Kids, a high school jazz group, delivered something more than just a cute interlude. With a 12-piece front line, and four more lines behind, the total number in the group surpassed 60. On standards like "On Green Dolphin Street" and "Watermelon Man," they turned out a full band sound and succinct, practiced solos. Their concentration was a reminder that collective rhythm is one of the most difficult but central aspects of jazz expression, whether the focus is on speedy skill or a playful dismantling of the restrictions of time.