SOME words are grossly over-used in the sporting universe. "Hero" is one, "iconic" another. But no word except "iconic" will do to describe the image of American athletes Tommie Smith and John Carlos after receiving their medals at the 1968 Olympic Games, in Mexico City 40 years ago this week, fists raised and heads bowed to draw attention to racial inequality back home. And no word but "hero" will do for the gold-medallist Smith in particular. The 24-year-old had just established a new 200 metres world record, but was prepared to sacrifice sporting achievement on the altar of civil rights, well aware that his moment on the podium would eclipse his 19.83 seconds on the track.

Nothing else that happened at the 1968 Olympics, not Bob Beamon's record-breaking long jump, not Dick Fosbury's new-fangled high jump – caught the world's attention like that so-called "Black Power salute" in what was already a convulsive year for protest statements. Martin Luther King and Robert Kennedy had both recently been assassinated and in Mexico City itself, just 10 days before the Games, more than 200 student demonstrators had been massacred by soldiers. Smith headed down to Mexico feeling charged by the electricity of the times.

On the day we meet, in the heartbreakingly prosaic surroundings of the Novotel, Euston Road, he is feeling a different kind of charge. It is a few hours since Smith, now a retired sociology professor, arrived in London from Atlanta, Georgia. He reached England with his wife but not, thanks to Delta Airlines, their luggage. So they have just been in the West End shopping for clothes, not the easiest or cheapest of tasks for a 6'4'' man aged 64. His credit card has taken a hammering and, what with the jetlag and all, he could be excused a certain shortness of temper. Yet he is the essence of genial politeness. Can he give me the background to what the world knows as the Black Power salute, but to him remains the "victory stand"?

"Sure," he says, taking a long, fortifying slug of coffee, into which his wife, Delois, has heaped about eight sugars. "I'd got involved with the Olympic Project for Human Rights, which was developed at the University of San Jose State, and saw the need for young black athletes to get involved in social change. And at a meeting held in Denver, Colorado, en route to Mexico City, we took a vote on whether we should actually boycott the Olympics. We voted against, but Ralph Boston, the great American long jumper, said 'what are we going to do instead?' We agreed that each athlete would represent themselves according to how they felt about a country that didn't represent them fully, and some chose to go ahead with their own personal boycott. The great basketball player Lew Alcindor, who later became Kareem Abdul Jabar, did not go.

"You see, hate was so entrenched in America at that time, and it took lives. White lives also. It took the Kennedys, Martin Luther King, Malcolm X, and many people we don't even know."

By October 1968, the deaths of two of their champions, King and Bobby Kennedy, had left African-Americans feeling even more disenfranchised than before. Smith, who had grown up one of 12 children of a poor Texan farmer hardly expecting to reach a position of influence, at least had the franchise of a global television audience. But to exploit it he had to finish in a medal position.

"I don't know what would have happened had I not won the gold medal," he tells me. "And I had a pulled muscle, so I was not the favourite. But I did win, and John Carlos won bronze, with [the Australian] Peter Norman in second place. We were then escorted to a place known as 'the dungeon' to prepare for the medal ceremony, and that's where John and I decided what we would do. Peter listened, but he didn't have much to say because this was an American situation."

Nonetheless, Norman lent his support by wearing an OPHR badge, unwittingly writing himself, too, into the history books. When he died, in October 2006, both Smith and Carlos were pall-bearers at his funeral.

During the medal ceremony, however, all eyes were on the two Americans, who wore one black glove each. Smith had his right fist raised, Carlos his left. It was later claimed that Smith's right fist denoted black power, with Carlos's left fist representing black unity. The slightly less stirring truth is that the gloves were Smith's, and they only had one pair between them.

"I had gotten my wife to send them from California, though I didn't know how I was going to use them," he says. When did he raise his arm? "As soon as I could recognise the first key of the national anthem. The crowd were completely silent." A short chuckle. "Silence is golden, you know." And with the ceremony over, then what? "Then what? I had to get off the victory stand and get the heck out of Dodge."

The reverberations began almost immediately, with Avery Brundage, who had represented the United States in the 1912 Olympics and was now the reactionary 81-year-old president of the International Olympic Committee, conducting the chorus of disapproval.

The smile fades from Smith's face when I mention Brundage. "Avery Brundage was a racist. He had admired the SS at the 1936 Games in Berlin and he hadn't changed one bit. But all he could do was denounce me verbally. As IOC president he had no jurisdiction over the American team. But he forced Douglas Roby, the president of the United States Olympic Committee, to do his dirty work. He told Roby that the whole team could be disqualified unless I was sent home. So that's what Roby did, kicked us off the team and sent us home. And to this day I am not a member of the USOC hall of fame, and nobody there will admit that what they did was wrong. They say 'I wasn't there, I wasn't even born'. They do not have the backbone to do what is necessary."

Smith says all this quietly and without obvious rancour; even his moral indignation is cloaked in geniality. "Bob Beamon wore black socks," he tells me, when I ask whether other black American athletes registered defiance in any way, "but the entire four by 100 relay team did nothing. Two of them, Mel Pender and Charlie Green, were in the army and would probably have been court-martialled. Jimmy Hines didn't do anything. He said the gold medal was going to make him a million dollars. He thought America was going to embrace them. It didn't work out that way."

If America failed to embrace those black athletes who didn't protest, it positively shunned those who did. "I started seeing the backs of people more than their fronts," says Smith. "I held 11 world records at the time of Mexico City, more than any man or woman in track and field history. In fact two still stand because they're not run any more – the 220 yards on the straightaway (ie run straight), and the 200m on the straightaway. So I was a hot item back then, but when I came back from Mexico, I was too hot. And people didn't want to feel the heat."

Smith and Carlos were widely denounced for showing "disrespect" for the American flag. The Associated Press report had described their "Nazi-like salute", and for Brent Musburger, the influential columnist in the Chicago American newspaper, they were "black-skinned stormtroopers". Smith, who was also in the army, was granted an honourable discharge for "unAmerican activities" and the surprise was only that it was honourable.

For months after he got home, he received abusive phone calls and even death threats. While some of his countrymen were refining the technology that would soon put a man on the moon, others were phoning in the dead of night and calling him an "uppity nigger". In 1970, Smith's mother died of a heart attack, aged 57, not long after she had been sent dead rats in the post. He is entitled to an enduring sense of grievance.

Yet he must surely feel some satisfaction now when he surveys the political landscape in America, and sees a black man seemingly within a month of becoming president. And did he not, in his own way, contribute to the conditions in which Barack Obama now prospers? "Do I feel satisfaction? No, because satisfaction implies satiation, and I do not feel sated. There is a lot to do still, but black athletes don't stand up for anything much any more, because million-dollar contracts have bought their souls. I am pleased that Obama is a man of colour, of course I am, but he is not there because he is African-American, he is there because he is a good politician. He needs more than colour."

Has he met Obama? "No, but you'd better believe I'd like to, though I don't think I'll be getting in my raggedy Chevrolet van to drive to Washington and say 'hey dude, what's happening?'"

So who did he meet as a result of his fame? What about the most decorated black American Olympian of all, Jesse Owens? "I wrote him a letter, shortly before he passed [away]. But Jesse Owens was like my dad. He stayed in his place as a black man. He couldn't afford human aspirations. And America liked that. Even now, America looks positively at the 1936 Olympics, when Jesse made Hitler mad, and negatively at the 1968 Olympics."

Having effectively put a match to a dazzling athletics career with his actions in Mexico City, in 1969 Smith joined the Cincinnati Bengals as a wide receiver, where he stayed for three years before pursuing a career in education. "No black man was involved in hiring me," he explains. "It was [the coaches] Bill Walsh and the legendary Paul Brown who took me to Cincinnati. I wasn't just helped by black people." A pause, and a chuckle. "But of course they weren't looking at my idealism. I was 6'4'' tall, weighed 205lb and ran [200m in] 19.83."

He must, I venture finally, have enjoyed Usain Bolt's Olympic exploits? Smith makes a noise that can only be described as a coo. "Oh my, yes. And ooh, would I love to coach him. I can see areas where he can improve, oh my goodness, yes. He's 6'5'' but in many ways he runs like a man of 5'10''. Puma gave him a big birthday party, which I went along to because he's a Puma man and so am I. They gave me a replica of one of his gold shoes, which he signed, and I gave him a red one of mine."

I leave the obvious unsaid, that the item that really symbolises the impact Tommie Smith made as an athlete, is not a red shoe, but a black glove.