Usain Bolt: Can the legend sign off with London 2017 World Championships win?

"It's not going to happen," replied Bolt when asked about the prospect of defeat at his media conference on Tuesday

Slower, later, weaker.

For a man who has lived the Olympic ideal of faster, higher, stronger, they are strange words to attach to Usain Bolt.

On Tuesday, at the front of a glitzy news conference, the media circus was called to attention, with the eight-time Olympic champion pulling his 'to the world' pose under a shower of ticker tape.

Above him shone the slogan 'forever fastest'.

It was a subtle, but telling, change to his sponsor's usual 'forever faster' tagline.

For Bolt is now pushing boundaries through sheer weight of gold-medal metal rather than an ever-lighter imprint on the clock.

His fastest 100m time so far this year is 9.95 seconds.

At the same stage last year - in the build-up to the Rio Olympics - he had run 9.88.

Before the World Championships in Beijing in 2015, he had clocked 9.87.

Heading into Moscow 2013, his best was 9.85. Before London 2012, it was 9.76.

Usain Bolt will sport gold spikes in London in an echo of Michael Johnson's famous footwear at the 1996 Olympics

Each time, he improved to win gold, but in progressively slower times as the years advanced.

That 9.58-second scorched-earth world record from Berlin 2009 belongs to the same man, but a different, irrevocable era.

Bolt, now 30, comes into this London edition of the World Championships, not as a sensation heralding a revolution, but instead hanging onto his empire against the challenge of Father Time and young pretenders.

With three rounds of the 100m, roughly 30 seconds of action, left of his career, could Bolt, weighed down with 19 World and Olympic gold medals, possibly bow out in defeat?

The men who would be king

Bolt may never have been slower before a major championship, but the threats to him have rarely been less clear.

The fastest man this year is Christian Coleman.

The American's best of 9.82 seconds was one of six occasions on which he dipped under 10 seconds this season.

Just 21, Coleman's expanding portfolio of performances attracted a seven-figure sponsorship deal from Nike as the sportswear giant made him their bet as Bolt's long-term successor.

Coleman has a marked lack of major championship experience however.

He told the Daily Telegraph that he was "pretty much a deer in the highlights" at the Rio Olympics where he appeared in the heats of the 4x100m relay.

The final of the United States trials - the biggest race of his season - delivered only his fifth-fastest time of the year and second place.

Still a student at University of Tennessee, Coleman will join the professional circuit full-time next season

Bolt's old sparring partner Justin Gatlin was the man who beat Coleman.

The 35-year-old claims he feels back to his 100m heyday when he won Olympic and world titles in 2004 and 2005, a time predating both Bolt's emergence and his own two doping bans.

He will need to be.

He has only beaten Bolt once in his long career - at a Diamond League meeting in Rome in 2013.

By contrast in major finals in 2012, 2013, 2016 and most notably at the world championships in Beijing 2015 when Gatlin came into the final faster and favoured, he was left in the Jamaican great's wake.

Yohan Blake is the second fastest man in the world this year - and of all time, behind Bolt.

He profited when Bolt fouled out of the 2011 World Championships and did the 100m-200m double in his compatriot's absence in the Jamaican trials this year.

But the 27-year-old has been hindered by a run of injuries in recent seasons and pulled out of the Diamond League meeting in Rabat in mid-July with a groin problem.

If Nike plumped for Coleman, Puma - Usain Bolt's own shoe sponsor - signed up Andre de Grasse in a multi-year, multi-million deal in 2015 as their pick for the next 100m superstar.

It seemed a good choice when the Canadian won bronze in Rio last summer. Less so this season however. Having struggled for form - he is only the 23rd fastest in the world - he has now pulled out of London 2017 with a hamstring tear.

• Podcast: How Bolt changed athletics

Analysis

Former 1500m world champion and BBC Sport commentator Steve Cram

Usain Bolt would not have given this field a second thought two or three years ago. He is not as good as he was. But he doesn't have to be.

Whatever we have seen so far, he will be better in London.

And what we have seen so far, in my opinion, is not that bad.

In Monaco, where he ran his season's best of 9.95 seconds a fortnight ago, I thought he looked pretty good.

I don't think he has been pushing harder than he has to to win so far this season - he has been steady out of the blocks, getting up to speed, pulling clear and then throttling off.

He has managed to adapt the demands he makes on himself pretty well in the last few years.

You also have to look around. Bolt is not as fast as he was, but where is the threat coming from?

Coleman is a bit of a raw talent without the experience that counts for so much in major finals. Blake has had a couple of injuries, and then you come back to the same-old in Justin Gatlin.

South Africa's Akani Simbine has been under 10 seconds eight times this season, but has tended to run his fast times early in the season at home and then has not reproduced in major finals. There would be a lot of people very surprised if he stepped up to that level.

I would always rather be in Usain Bolt's camp than anyone else's.

Exit stage centre

Maybe London 2017 doesn't really matter anyway.

Less than victory would end Bolt's gold run in the blue riband event, but it would be a blemish to bother only the most particular completists.

The specifics of Saturday's night final at London Stadium will slowly fade to footnotes on Bolt's career.

It won't be the heap of titles or spreadsheets seconds, but yawning winning margins as wide as Bolt's grin that define his legacy.

Bolt was a wide-eyed 21-year-old when he won 100m gold in Beijing in 2008

Before Bolt arrived, sprinting was a serious, testosterone-soaked business.

The likes of Linford Christie, Leroy Burrell, Maurice Greene and Donavon Bailey snarled and strutted on the start-line, as quick to take offence as they were over the ground. Bolt ushered in an era of slacker-chic.

He shunned the twitchy thousand-yard stare and instead clowned his way to greatness. And his rivals have, for the most part, aped his example.

Bolt's connection with fans has made him a crossover star far beyond athletics

He has rewritten not just record books, but sprinting etiquette, transforming the culture of the sport's headline event.

Crucially Bolt's performances have been as natural as his act.

After former relay team-mate Nesta Carter tested positive for a banned substance in January, only nine of the 33 fastest 100m times in history remain untainted by drugs bans.

All were run by Bolt.

On Tuesday, he warned that if doping continued it could undermine the public's faith so fatally that athletics as a whole could die off.

Whether fellow athletes heed that call to save the golden goose or instead cheat their way towards the vacuum he leaves behind, only time will tell.