There, as he paces and glances, and rolls his enormous shoulders, the self-styled Kansas Cannonball gives a rare public glimpse of the qualities that have fired him to the top of the sprint world rankings.
Yesterday, however, appearing in London to publicise the first appearance of what he hopes will be a successful Olympic season - at the CGU Indoor Grand Prix in Birmingham on 20 February - his broad smile flashed as often as the diamond in his left ear-lobe.
Greene had every reason to be in a sunny mood, having accepted his award as the British Overseas Sports Personality of the Year at BBC TV centre shortly before Lewis was announced as winner of the main Sports Personality award, and Muhammad Ali was honoured by being named the Sports Personality of the Century (or was that the Millennium?).
He speaks publicly now with practised ease, unrecognisable as the figure whose shy public utterances in the wake of his 1997 world 100m victory, laden with references to the Lord, were so cruelly mocked by the Canadian beaten into second place, Donovan Bailey.
But if his words are standard, his performances over the last two years have been superlative. At 25, Greene can lay claim to three individual world titles - at this year's world championships he became the first man since the great Carl Lewis to win a 100-200m double at a global championships - and he also holds the world records at 60m (6.39sec) and 100m (9.79sec).
Since he upped sticks and joined John Smith's training group in California following the disappointment of his failure to qualify for the 1996 Olympics, Greene's trajectory has been dramatic. He now stands undisputed as the best sprinter in the world, with a 100m time that has finally matched that set at the 1988 Olympics by Ben Johnson, whose performance was subsequently annulled because of doping abuse.
Greene accepted that Johnson's current status - a drifter on the edges of the sport who is now earning a living assisting the ambitions of Colonel Gaddafi's son to play football for Libya - is regrettable. "It's very sad," he said. "But I don't worry about what he is doing." It has not escaped his attention, though, that his 9.79 was recorded with less wind speed than Johnson's, making it - since you ask - superior.
This small correction serves also to point up the obvious fact that you do not get to be where Maurice Greene currently stands just by being pleasant. He is known by his colleagues as being a fiercely motivated trainer. "To be No 1, you must train like you are No 2," he said yesterday. "Otherwise you have no place to go."
Greene knows well enough that he is in danger of trapping himself by his own excellence. His aim now is to knock a couple of hundredths off both his 60m and 100m times, although Smith has said he believes a 100m of 9.6sec is possible.
His other ambition of meeting - and beating - the Olympic 200m and 400m champion, Michael Johnson, over the shorter of those two distances is a vexed area.
Johnson, who did not contest the 200m at the last US trials, has resisted suggestions from Greene's camp that he take part in a race with their man to settle the argument of who is really the world's fastest runner.
"Michael doesn't talk to me,' said Greene with a sly grin. "You'll have to ask him why. He used to do. But now if I walk in the room, he'll walk out. I have no need to talk to him, though. If he wants to race me, he knows where to find me..."
In the meantime, however, Greene is concentrating his attention on next year's Sydney Olympics, where another 100m-200m double looks distinctly possible. And he takes with him the inspirational memory of the sportsman he has most admired - not Ali, but the all-time record-breaking running back Walter Payton of the Chicago Bears, who died last month of cancer aged 45.
"I just admired everything about Walter Payton," Greene said. "When I was growing up watching American Football, and I was playing it at high school, I wanted to run the ball like he did. One thing I always enjoyed about him is he never wanted to go out of bounds, he always was striving to go forward, to keep pushing forward to get yards. And I just loved that in him. I mean... he was a tough contender."
Greene might have been speaking about himself. It is little wonder Johnson is boxing clever.Reuse content