She is claimed to have spent more than 650 hours in rehearsal for her world tour.

But on the opening night, it was the time Madonna had spent pumping iron in the gym which had the most dramatic results.

As she gyrated in Cardiff on Saturday, the Queen of Pop's raunchy stage outfits showed off her bulging thighs and biceps.

Fans paid up to £160 for tickets to Madonna's first world tour since Confessions in 2004, although the Millennium Stadium was far from full.

Madonna kicks off her highly anticipated Sticky & Sweet Tour promoting Number One album Hard Candy at the Millennium Stadium in Cardiff

They also had to show patience, with the show starting more than 90 minutes later than billed. So was it all worth it?

The last time Madonna played in Cardiff, she opened her Confessions tour by arriving on stage in horse-riding gear.

She then spent the evening turning the Millennium Stadium into the world's biggest disco and causing controversy by posing on a crucifix wearing a crown of thorns.

Two years on, the opening sequences of her Sticky&Sweet tour were even more spectacular.

Amid a dizzying barrage of computerised graphics, the Queen of Pop, in leather boots and figure-hugging pants, greeted her Welsh subjects by sitting imperiously on a futuristic black throne.

She then underwent eight costume changes which saw her return to the stage as a pole-dancing, break- dancing cheerleader and later as a gipsy singer with a travelling band of minstrels.

Cheeky: Madonna teases the crowd

Nobody does a big stadium show quite like Madonna. She might be pop's greatest female icon, but she does not rest on her laurels and this was a theatrical, two-hour blockbuster, featuring 16 dancers and a 12-piece band.

This time, too, there was no need to resort to any shock tactics. If any of the 40,000 crowd had come along expecting any off-piste, Amy Winehouse moments, they would have gone home disappointed.

Madonna doesn't do spontaneity.

She is pop's consummate professional and the 653 hours of rehearsals which apparently went into this tour were evident in some choreographed routines which were nothing short of breathtaking.

Remarkable: Madonna made rubber-limbed gyrations - despite turning 50

The fact that the singer turned 50 earlier this month made her rubber-limbed gyrations all the more remarkable. 

If the Confessions tour was a no-holds-barred journey out on to the dance floor, the current show is more diverse.

Perhaps keen to reinforce her musical legacy there are more crowd-pleasing older hits, with Into the Groove, Like a Prayer, Vogue and Borderline all featuring.

Even You Must Love Me, from Evita, gets an airing. Accompanied by just an acoustic guitar, it was forcefully sung and provided one of the night's more intimate moments.

With Madonna regularly strapping on a black guitar and bashing out some crisp but rudimentary power chords, the overall mood was more rock-orientated than previous tours.

For Madonna, a born actress, a musical instrument is the perfect prop and she struck plenty of guitarheroine poses.

Hung Up, originally a homage to Abba, began like the White Stripes on a bad night, but progressed towards a slick finale with Madonna miming the smoking of a cigarette while leaning nonchalantly against a speaker.

The high point was a vibrant La Isla Bonita, sung gipsy-style in a colourful throwback to Madonna's appearance at last year's Live Earth concert at Wembley.

The garbled video montage which accompanied Get Stupid was less coherent.

With the singer off-stage for a costume change, the two giant screens either side of the stage showed footage from war zones alongside images of John Lennon, Nelson Mandela, and, finally, U.S. presidential hopeful Barack Obama.

With the latter's face lingering on screen, we can take it that Madge will not be voting for John McCain.

The predominantly female audience, many in pink cowboy hats, had not come for guidance on American politics, however. They had come to party.

Their spirits were soon roused by a sassy 4 Minutes, with Justin Timberlake duetting via a pre-recorded video.

As is usually the case with Madonna, the asides to the audience were kept to a minimum. After an introductory 'All right, Cardiff?' nothing was said between songs near its end.

Then, after initially asking for requests from the floor, the singer snapped back: 'I'm in charge. I choose the songs.' 

It might have been better had she kept her mouth closed. After such an exhilarating show her comments, while jokey, seemed a little inappropriate. 

That said, on this kind of form she remains the show woman all the others still have to beat.