Occasionally, in the leafy surrounds of the Giardini, at this year's Venice Biennale, one hears a loud, clunking rattle, accompanied by the squeaks of heavily turning machinery. The sound comes from a tank outside the American pavilion. It is upside down – belly up, even – and it has been hooked up to a treadmill that sits on top of it. When the tank does crank into life, and its treads turn uselessly in the air, it does so because it is being powered by an American athlete, running on the treadmill while wearing a red, white and blue uniform.
The work is by the artists Allora and Calzadilla and it is part of their exhibition, Gloria, which is the American contribution to the Biennale.
Runners are always compelling to watch – visitors to Tate Britain might remember Martin Creed's athletes sprinting through the Duveen Galleries in 2008. But Allora and Calzadilla's work is more complex than its description might suggest. The way in which the figure (it was a man both times I saw the work) is dwarfed by the military machine, and yet puts all his energy into powering it, running himself into the ground, as it were, makes a political statement about America and war. Uncomfortably, however, the strong man and the strong machine are impressive in an enjoyable way. Inside the pavilion are gymnasts moving beautifully on airline seats and a video of athletes climbing poles, as though as to fly themselves like flags.
The reason that I mention the American pavilion first is that it is a particularly successful example of a feeling that is everywhere at the 2011 Biennale – anxiety about national representation and what this might mean. Guillermo Calzadilla was born in 1971 in Havana and Jennifer Allora was born in 1974 in Philadelphia. They are now based in Puerto Rico.
More than ever, the pavilions in the Giardini – an ornamental public garden filled with small, architecturally diverse buildings owned by the various countries (often old colonial powers), which artists "represent" during showtime – push and strain at their setting. Self-awareness pervades, and several exhibitions are based on the idea that artists have been asked to make a "national exhibition" at all.
In the Polish pavilion an Israeli artist, Yael Bartana, is showing a trilogy of films that she has been working on in Warsaw for some time. These works – which, aesthetically, resemble second world war propaganda films – imagine a political movement in which 3.3 million Jews are encouraged to return to Poland, thereby conflating and confusing the Zionist dream of a "return" to homeland with the complex and traumatic events of recent Polish history. There is something warm in these films, which sometimes resemble parodies, albeit made with kid gloves. Bartana keeps on the right side of sensitivity.
The Danish pavilion features a group exhibition on the subject of free speech and who gets to speak for whom. Eighteen artists contribute, including Taryn Simon (from the US), Tala Madani (Iran) and Jan Švankmajer (Czech Republic). Only two of the artists are Danish. The Egyptian pavilion features a work by Ahmed Basiony that places footage of the artist running on the spot, while wearing a specially constructed suit that measures his body's output of heat, next to his last pieces of footage, which are of the demonstrations in Tahrir Square, where he was killed on 28 January.
Several countries have contributed large-scale installations. In the British pavilion, an overwhelmingly immersive work by Mike Nelson transports visitors to a dusty 17th-century caravanserai building from Istanbul. It is a work that gives a more oblique nod to issues of cultural identity and power.
The German pavilion features an altar-like space from which to view several films by Christoph Schlingensief, who died of cancer before he could complete his work on the exhibition. The Swiss artist Thomas Hirschhorn has created one of his signature foil tunnels, filled with televisions, toys, detritus, tape and political slogans.
France presents work by Christian Boltanski, who has created a cold machine in which monochrome photographs of babies' faces travel around an enormous architectural scaffold. To one side is a green figure, tolling how many people have been born that day; at the other side is a red figure, counting the number of people who have died. It seemed to me a pretty trite statement, suffering from theatrical grandiosity. On the other hand, I enjoyed immensely the Australian contribution from Hany Armanious, whose sculptural casts of everyday items such as pinboards, plinths, Burger King crowns and broken window blinds raise the prosaic into a moving aesthetic experience.
Among the off-site exhibitions worth seeing is Karla Black's explosion of immense pastel works made from paper, polythene, sawdust and dirt, at Palazzo Pisani for the Scottish Pavilion. Black's exhibition culminates in a kind of messy, lovely floorwork in which soap, soil, make-up and glitter look like a cross between a beautiful garden and a dumping ground. The Palazzo Zenobio houses ArtSway's New Forest pavilion, which showcases the work of artists who have had residencies there. Gayle Chong Kwan's diorama photography and Christopher Orr's painted miniatures stand out. Also in the Palazzo Zenobio, in the Pavilion of Iceland, is a video of a musical piece by Libia Castro & Ólafur Ólafsson on the theme of stateless people, which was performed on gondolas around Venice.
Also on offer is the 54th International Art Exhibition. If the title of the show – ILLUMInations – is a clunky mix of cases and concepts, it is nothing like the show itself, which is rather beautiful and intellectually refined. The exhibition is curated by Bice Curiger, a founder and editor-in-chief of the elegant and thorough art journal Parkett and publishing director of Tate Etc magazine, and so there's not a huge amount of surprises as far as the artists included are concerned; many have been featured in Parkett over the years.
This is one of the most cohesive shows I have seen. It tackles issues that relate to a distinctly modern experience. These include a kind of cold, machine-like modernity, which is seen in the photographs of photographs by Annette Kelm and the eerily tight, catalogue-like images in coloured frames by Elad Lassry. This meeting of artistic and machine processes can also be seen in the works of several American artists. Christopher Wool, Josh Smith and Seth Price, for example, employ a kind of smashed-together, multilayered practice that combines print, painting and sculpture and which might involve takeaway menus, inkjet printers, paint and vacuum-formed plastic. Machines often seemed to be the ones looking at one another here, as we, in turn, looked on.
A form of confused internationalism is also present in Song Dong's miniature pavilion within a pavilion, created from junky mirrors and old cupboard doors, in which works by Yto Barrada and Ryan Gander have been installed. Monika Sosnowska's aggressively confusing wallpaper structure, housing David Goldblatt's photographic chronicling of criminality, architecture and everyday life in post-apartheid South Africa and a disturbing jumpy sonic sculpture from the young British artist Haroon Mirza, creates another interesting meeting of atmospheres, ideas and histories.
Appropriately for Venice, which has the stuff in pale, gorgeous abundance, the play of light gives this exhibition its most memorable moments, from Curiger's use of Tintoretto paintings to the small, brightly coloured photographs of accidental beauty in everyday life by Luigi Ghirri – including trees that seem to tickle a woman's image on a billboard. RH Quaytman's paintings create gorgeous, throbbing waves of light and glitter by placing classical imagery together with op art painting techniques. These are moments that shine and lift.
So too do Jean Luc Mylayne's huge photographs of tiny, bright birds, caught for a flicker of a second on film; Carol Bove's sculptures, made of metal, light and foam and installed on a tall plinth above viewers' heads, seem to float out of reach; and Monica Bonvicini's glittering transparent stair sculptures, which resemble steps to a cold, classy heaven.
While the exhibition may teeter on becoming overly formal and neat at times, such moments of glorious loveliness are reminders of why we are even here at all.
Venice Biennale 2011 National Pavilions and ILLUMInations ( www.labiennale.org) to 27 November 2011
Three to see: the alternative Venice
The Venice Biennale is worth the trip, but some of the most memorable works are not in the Giardini but at the Arsenale, a former naval dockyard by the Grand Canal. These three will linger in the memory, for better or worse.
Hans Op de Beeck
The Belgian artist's unforgettable and haunting work, 'Location 7' shows a normal, western-European suburban home after a Vesuvius-type eruption has covered everything in ash. It's Pompeii in the Home Counties. Furniture, blades of grass and the baby's cot are all turned to concrete and rendered in grey monotone.
I loved the Indian artist's 'Elevator from the Subcontinent'. You press the button of what seems to be a lift and a door opens – you are now inside a space in which video screens move down, giving the illusion of a lift taking you skywards. The screens show life in the Indian metropolis and the viewer 'ascends' through different strata of society. A novel and affecting way of presenting an artwork – though some found it too claustrophobic.
The Swedish artist won an award at the weekend, for her contribution to the Biennale – 10 rubbish bins from different countries. So is this stunning and prize-worthy contemporary art? Or is it, in line with its subject matter, rubbish? Make up your own mind. As one of many who very nearly disposed of some litter in one of Liden's masterpieces while absent-mindedly walking past, I'm afraid I didn't immediately recognise its artistic value.