Bolt retired after the 2017 worlds, taking a haul of gold medals and jaw-dropping world records of 9.58 seconds in the 100 and 19.19 in the 200 with him. A star factor impossible to replicate, let alone replace, also left the sport.
"In my lifetime watching sport, I can't think of anybody other than Muhammad Ali that has had such an extraordinary global reach," Coe told The Associated Press in an interview Sunday. "Usain was what he was, not simply because he has a sack-load of medals and lots of world records. He was because he has a personality and that's the other thing we really make sure the athletes understand. Yes, they are in sport but their business is entertainment."
However, the head of track and field's governing body - who won Olympic golds in the 1,500 in 1980 and '84 - hopes emerging young athletes make their own mark at the Sept. 27-Oct. 6 worlds.
"I don't think it's particularly healthy for a sport to rely on one person, however unbelievable the status is," the 62-year-old Englishman told the AP at a Paris hotel - one day after the city held a Diamond League meet. "I take a lot of comfort from the prevailing group of athletes. I mean, Noah Lyles last night was a very good example (winning the 200) in 19.65 seconds."
Lyles is 22 years old and a strong contender to win gold for the U.S. in Doha, Qatar. But his highly rated countryman Christian Coleman may not even compete there.
Coleman risks a doping suspension which could rule him out. Coleman has the year's leading 100-meter time with 9.81 to go with world-leading 100-meter times last year and in 2017. At the 2017 worlds he finished second to Justin Gatlin and ahead of third-place Bolt.
But the 23-year-old faces allegations he missed three doping tests over a 12-month period. He said he expects to be cleared when the U.S. Anti-Doping Agency's arbitration panel rules on Sept. 5.
"My absorption of what he is saying is that he will be able to make a strong case as to whatever the issue is. I don't think there's much more I can add," Coe said. "Timing's not great of course, but I'm not going to speculate about something I have no insight into."
PROGRESS ON RUSSIA
In a wide-ranging interview with the AP, Coe addressed other issues - such as the Russian doping scandal and Caster Semenya's case.
IAAF leadership previously faced criticism over its handling of widespread doping in Russia, which remains banned from international track and field, though dozens of top Russian athletes compete as neutrals.
Progress appears to have been made.
Rune Andersen, the head of the IAAF's Russia task force, welcomed a long-awaited payment of $3.2 million to cover costs of monitoring its compliance with anti-doping rules, and old doping samples have been made available for checks.
Russia's anti-doping agency, RUSADA, was reinstated by WADA last year. Since then, RUSADA has increased drug testing and pursued high-profile investigations such as that of high jumper Danil Lysenko - who allegedly presented forged medical documents as an alibi for failing to notify drug testers of his whereabouts.
"I think this is moving in the right direction and the outstanding issues are significantly less than they were," Coe said. "The new federation has made good progress, there's no question about that."
Not everyone agrees, even in Russia.
Mariya Lasitskene, a two-time high jump world champion, wants the country's officials and coaches in the sport replaced because of slow reforms.
Also, 12 Russian weightlifters were recently charged with doping offenses stemming from WADA investigations covering the last decade.
WADA has been analyzing a vast archive of data finally obtained in January from the anti-doping laboratory in Moscow, where cases were routinely covered up for years. The data has been sent to the IAAF's Athletics Integrity Unit.
"I am advised it is like going through 51,000 CDs," Coe said. "The AIU are painstakingly going through this."
Russian athletes will compete as neutrals in Doha, unless an unlikely decision to reinstate them under the Russian flag is made in time.
"I suppose technically they could. I'm not speculating," said Coe. "We will wait to see where the task force gets. We will get another report (in Doha before the worlds)."
CHANGES OF ALLEGIANCE
Bahrain, Qatar and Turkey will compete with squads of elite African-born runners.
Countries spent years recruiting them until the IAAF tightened rules for changes of allegiance, fearing athletes were being bought and sold. The new measures include a three-year waiting period, a ban on athletes transferring more than once, and no transfers for those under 20.
Coe recalls the chaos surrounding allegiance switches before the 2016 Olympic Games in Rio de Janeiro.
"An email would arrive to the (IAAF) council. It would say 'The Federation of X and the federation of Y have agreed the transfer of allegiance and if we don't hear from you in 36 hours we presume you're OK with that.' In one day, we had 23 applications and I (thought) 'This cannot be right,'" Coe said, sounding exasperated. "I live in a global world and I am mixed race, I have a lot of Indian ancestry, grandparents, and so I recognize there are exceptional circumstances.
"Sometimes an athlete can be in a climatically challenged environment or you can be in a war zone," Coe added. "You can't have athletes being traded, it's bordering on trafficking if you're not careful. I've had member federation presidents who have said to me openly that they were waking up to emails from people saying 'We've got so and so (who) is available for ...' You can't have that."
A contentious decision was made preventing Caster Semenya from defending her title in the 800 meters at the worlds. She won't do so because a Swiss court overturned a temporary ruling allowing her to compete without testosterone-suppressing drugs.
The 28-year-old South African is fighting the IAAF over rules requiring her to take the drugs to counter her naturally high testosterone levels. Semenya was legally classified as female at birth and has identified as female her whole life. She was born with the typical male XY chromosome pattern and a condition that results in male and female biological characteristics and testosterone higher than the typical female range.
The Swiss Federal Supreme Court reversed a ruling that temporarily threw out IAAF regulations also upheld by the Court of Arbitration for Sport.
"We made the judgment on what we felt was the best interest of the sport. It was probably inevitable there would be some challenges," Coe told the AP. "I don't think we were particularly surprised by that, and we remain confident that the regulations we have tabled are the right regulations."
Qatar, where October temperatures hit 35 degrees Celsius (95 Fahrenheit), is feeling political heat amid an ongoing Gulf diplomatic crisis with Saudi Arabia, Bahrain and the United Arab Emirates.
"People say 'Well it's a bit warm (there) and I'm not sure about the political structures,'" Coe said. "Well, I'm not sure everybody who came to the London Olympic Games (in 2012) approved of our foreign policy, but they still came."
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