Tomorrow, Parisians will line the fashionable streets and wave flags for an American procession, as though it were Liberation Day all over again.

Lance Armstrong's iron domination of the Tour De France has to rank as the most formidable and impressive sporting feat of our time and he has been compared to icons as diverse as Ali and Seabiscuit. But as he claims the yellow jersey for the seventh and final time tomorrow, the abiding sense is of a phenomenal human being whose savage brilliance has somehow shrunken rather than illuminated his sport.

The more you hear and read of Armstrong, the harder it is to form any conclusive impression of the man. There are two obvious dimensions to the Texan's public persona. His titanic, uncompromising battle against a particularly aggressive form of cancer has understandably rendered him a hero for people who might otherwise have no interest in cycling. And he has used his sporting prowess and fame to spearhead a highly lucrative and beneficial series of charity drives which have helped others, most potently through his yellow wristbands bearing the legend Live Strong.

Armstrong's illness occurred in his early 20s, just when he had become one of the youngest winners of a Tour stage. As his best-selling memoir, It's Not About The Bike, described in candid detail, Armstrong's bravest performance took place in his sickbed. When he returned to professional racing less than two years after a prognosis that suggested the grimmest resolution, he was already halfway transformed into a mythical and unbeatable figure.

Given his fellow competitors couldn't but know the details of his illness, they must have been psychologically ruined before they even lined up alongside him. If Armstrong could brush off the spectre of death, how could they hope to intimidate him in any way? And as he demonstrated his seemingly limitless capacity for performing through pain, smashing the pain barriers of cycling, it became clear the American was not merely content with excellence in his own lifetime but was intent on making a statement through cycling that may never be surpassed.

In the late 1980s in Ireland, professional cycling was a rainbow through the gloom, and the exploits of Seán Kelly, Stephen Roche, Martin Earley and Paul Kimmage made Tour buffs out of practically everyone. For four or five Julys, the Tour became household television viewing. Back then, it was hard not to feel pride when Kelly's toughness and appetite for road was favourably compared to the legends of yesteryear like Bernard Hinault and Eddie Merckx. And even now, the grainy recording of Roche appearing on the summit of the hill after the misty climb through the mountains when he was supposedly lost holds the power to give you the shivers.

But the granite compression of the Texan's achievements now stands over all previous eras in the 100 years of the race. Attitudes towards him in France appear to be mixed at best. Part of the reservation is almost certainly based on jealousy and the fact an American has taken an immortal grip on one of France's most cherished cultural trophies. It is also because he has elevated the emphasis on team, commanding unquestioning obedience from his support riders and approaching each stage with a disciplined tactical regimen which seemed to lack the free-wheeling spirit that native fans sought from the race.

As Armstrong caught up and then began to surpass the rare trinity of five-time Tour winners, he tapered his annual schedule to peak solely for the French prize. While Merckx finished first in 250 of 650 starts between 1969 and 1973, Armstrong only enters around 60 or 70 races per year.

But because of his inspirational personal story and relentless winning record, he has broken into the market generally reserved for the traditional ball sport stars in America, matching Michael Jordan in terms of commercial endorsements. When Greg LeMond won three Tours in the late 1990s, America paid lip service but cycling and LeMond was regarded as a cult interest.

LeMond, though, has been the most conspicuous critic of the probity of Armstrong's achievements, publicly casting doubt after his fellow American was linked to disgraced Italian coach Michele Ferrari.

The issue of substance abuse has shadowed Armstrong more tenaciously than his competitors ever could and although he will bow out of the Tour without having failed a drug test the accusations remain. Soon, he will turn his energies into taking a libel case against a book entitled La Confidentiel, an incriminating examination of Armstrong's career history part authored by Irish journalist David Walsh, one of the American's most outspoken critics.

Perhaps that is one of the reasons it has been difficult to fully engage with what is, on principle, a truly monumental realisation of human spirit and potential by Armstrong.

In the days since we in this country were held spellbound by the heroics of Roche and Kelly, cycling has become a ghost world and the sad death by suicide of former champion Marco Pantani was like an indictment of everything cycling stood for.

As with all sports that flirt with the far end of human endurance, there were always murmurs. As Jacques Anquetil famously complained when the subject of illegal substances was raised, "Do they expect us to ride up these mountains on mineral water?"

Even after the poor English man Tom Simpson fell and died of a heart attack in 1967, the vast majority wanted to believe that cycling and the Tour de France was the stuff of rare valour, a race for those few blessed with warrior souls.

That assumption has been torn apart in the last 10 years and it has been in an atmosphere of doubt and recrimination, during a period when cycling has been branded as diseased, that Armstrong has made his statement. It has not helped that through all his winning years, he has stayed remote, that he has never seemed to need the galleries that lined the country roads to witness him pass in a flash of yellow.

So, given the pattern of modern sports, it seems best to reserve judgment now, to wait and see if a deeper story doesn't unfold. Like baseball's troubled sluggers or the beleaguered stars of track and field, the Texan may yet come to understand that the parched and exhausting races, the lung-bursting mountains and deadly descents, were almost trivial in comparison to the struggle to keep his reputation from getting sucked into the murk.

The best we can hope for is that Armstrong's brilliance just coincided with a messy and paranoid chapter in professional sport and that, against all the odds, he was a paragon of virtue in a filthy time. But tomorrow, they will crowd the streets to view the unconquerable champion from the Lone Star State and while they will applaud his staggering legacy with wonder, deep down they will also wonder.