The revelation that Muhammad Ali secretly addressed a rally of the Ku Klux Klan will cause further debate about the legacy of the former heavyweight champion. The meeting is revealed by Ali himself in an interview in the build-up to his 1975 fight against Joe Frazier, and forms the focal point of True Stories: Thrilla in Manila, a documentary to be broadcast on More 4 tomorrow evening.

Ali's detractors will doubtless take the episode as further evidence of his divisiveness and hypocrisy. His admirers, though, will attribute it to the undue influence of his religious handlers in the Nation of Islam, a radical group whose avowal of a separation of the races converged with that of the Klan. It is well known that their respective leaderships often covertly met in search of an ultimately elusive pact.

The renewed debate about Ali comes at an opportune moment as the American media debates the wider significance of black athletes after the election of Barack Obama. Many have asserted that the sporting success of athletes such as Jesse Owens, Joe Louis and Jackie Robinson served to undermine the basis of white supremacy and, in the process, paved the way for Obama. As an analysis of the power of sport to change the world, it is stirring stuff. It is also almost entirely inaccurate.

The reality is that only a tiny fraction of white supremacists actually believed blacks were inferior athletes. The majority - including the eugenicists whose views were central to the construction of Jim Crow segregation - positively endorsed the notion of black physical superiority, arguing that it demonstrated the evolutionary primitiveness of the Negro. This helped to harden the stereotype of the black brute and provided justification for the continued use of blacks in the cotton fields of the rural South.

Why else did Jesse Owens's success at the Berlin Olympics of 1936 do so little to shake the intellectual basis of Aryan supremacy? Historians who have chronicled that episode have often argued that his success not only failed to undercut Hitler's propaganda coup, but actually bolstered racism within Germany. As Nazi intellectuals were quick to point out, Negroes had “abnormally large animal heel bones” and were therefore bound to be faster.

Similarly, Jack Johnson did not offend white sensibilities by defeating white men, but by cavorting with white women at a time when miscegenation was illegal across the South and by mocking his opponents with a swagger that led to rioting after his demolition of Jim Jeffries in 1910. Joe Louis, a boxer who defeated many more white opponents than Johnson, was actually embraced by many racists precisely because his success went hand in hand with the deference (cultivated as a deliberate fop to white America) that they demanded of an “intellectual and social inferior”.

In 1999, the extreme Right proclaimed the notion of black athletic superiority, lauding Jon Entine's book, Taboo, asserting the scientific basis of black sporting success. Liberals famili-ar with history of black suppression were appalled by the implications. As one writer put it: “The dubious idea that blacks are athletically superior is about confirming a broader prejudice that blacks are intellectually inferior: beasts of burden, dull and strong.”

This is not to deny the importance of black sporting success but to assert that its contribution to racial equality is more complex than is often claimed. Its central importance was not to undermine the intellectual basis of racism, but to bolster the self-esteem of a downtrodden minority. Sport was a focal point of ethnic pride because it was just about the only area of public life where blacks - protected from discrimination by sport's objectivity - could get ahead. In this sense, it provided a platform for blacks to strike at the true foundation of white bigotry: the myth of white intellectual superiority.

Which brings us back to Ali. He was unquestionably a polarising and deeply paradoxical figure, as the Klan episode testifies. But on the wider point, can it seriously be argued that his victories over the likes of Henry Cooper were his most crucial contribution to black emancipation given that blacks had virtually monopolised the heavyweight title for decades? Is it not more credible to contend that it was Ali's audacious demeanour and rhetoric, rather than his fists, that changed the tenor of that tumultuous era?

Like almost every great black athlete of the 20th century, Ali's political importance was revealed not in his sporting success or his errors of judgment but in the broader thrust of his words and deeds. It was his capacity to shatter the stereotype of black inadequacy that shook up the world, not his ability to shatter white men's jaws.