Dance: Among the dark balletic mills

Siobhan Davies Barbican, EC2 Wendy Houstoun Purcell Room, SE1

At a packed Barbican Theatre on Thursday night the audible intake of breath when the lights went down said much about the phenomenon that is Dance Umbrella. From small beginnings in 1978, the two-month international festival is now unfurling its 20th season, carrying with it a weight of expectation. What's the opposite of dumbing down? Sharpening up? Because that's what Dance Umbrella has done. Popularity hasn't led to any softening of its challenge. And there's no artist more demanding of her audience than Siobhan Davies, whose fine company opened this year's season with two works of uncompromising rigour.

Winnsboro Cotton Mill Blues is set to Frederic Rzewski's chugging piano score of the same title. Treating the piano's hammer mechanism as the shuttle of loom, it demands of the performer an ability to play chuntering, repeated chords with what sounds like 25 fingers. Davies extends Rzewski's music with taped sounds of a real Lancashire cotton mill, and translates the industrial theme upon her dancers' bodies in movements that evoke both the sweated labour of factory workers and the action of the machinery itself.

Peter Mumford's lighting is darkly satanic; at one point two heavy rigs of searchlights descend to oppress the troglodyte activity further. The 10 bodies muster into marching lines, or clump in formations of cogs and chains and interlocking shuttles, summoning the oily heat and slog of man and machine - it's unclear which is master. But as always in Davies' work, the human spirit prevails. Just as one's eye begins to be clogged by detail, a single dancer breaks out into curling, sweeping flight like a great bird being released through a small window. And it's this consummate control of timing and imaginative feeling that makes Davies' work so richly satisfying.

Those who hang around the auditorium during the interval will see the spectacle of Rex Lawson, world pianola expert, setting up his stall in the pit. If Davies had an ounce of showbiz in her soul she would have hauled him up on stage with his curious punched-paper scrolls and pedals and pulleys, not to mention his record-breaking 2ft beard. But no, he's there to reproduce a selection of Conlon Nancarrow's studies for player- piano (via a device that sits over the regular Steinway keyboard, driven by a handle).

This is piano music beyond the reach of mortals both in terms of speed and contrapuntal craziness. In one study, glissandi race up and down the treble keys in manic succession; others feature fractured boogie-woogie, ragtime or tango, which Davies's dancers don't so much dance to as through. Out of the music's arhythmic mayhem, the choreographer creates a kind of serene visual logic, with its own inversions and surprises. In the Siobhan Davies canon, this one is as abstract as they come (its title, Eighty Eight, refers to the number of keys on a piano). Yet again, Davies succeeds in harnessing the power of idiosyncratic movement to evoke experiences from the purely sensory to the near-metaphysical.

More down-to-earth but equally difficult to pin down, is Wendy Houstoun, once renowned for her daring as part of DV8, now performing solos of her own making. Wezza is something of a Bob Dylan in the dance world. Wild and curly haired, a maverick to the tips of her naked toes, she seems to reinvent herself for each new piece of work. And this time she's that long-term resident of the lounge bar, the pub slag.

Maid to Drink is a physical monologue on the theme of alcohol and its use as a social and emotional smokescreen. You prefer to think of drink as a tongue-loosener or an ice-breaker? Houstoun shows the ritual and cliche of the drinker's world as merely another kind of straitjacket. But first, she takes pleasure in giving the conventional theatrical experience a sly tweak. "What d'you want?" she asks us, "The usual ...?" Then, disconcertingly, after a flailing dance sequence based on clearing glasses and pulling pints, "This is a bit flat isn't it?"

Actually, it's daringly brilliant. We are treated to every scrap of half-baked, vodka-soaked, barstool philosophy in the book, spewed out in stream of bad jokes and platitudes while Houstoun wraps her rubber-band body around a makeshift bar, a stool, and eventually the floor. Only once, to some scuzzy disco music, does she give a glimpse of her legendary dance virtuosity; otherwise she subdues her technique to the liver-curdling task in hand, that of showing a martian what very strange behaviour we indulge when someone puts a glass in our hand.

Siobhan Davies Co: Manchester RNCM, (0161 907 5278), Fri & Sat; Birmingham Rep (0121 236 4455), 16 & 17 October.