“If I can make it there, I’ll make it anywhere, It’s up to you, New York, New York.”

In 2007, Paula Radcliffe won the New York City Marathon for the second time, less than ten months after giving birth to her first child, Isla. She said that repeating “I love Isla” over and over in her mind was the perfect mantra for her stride pattern as she ran the last agonising few miles.

As she crossed the line her eyes darted about the crowd looking for Isla. She draped a Union Jack over the child and pulled her as close as physically possible, a proud mother showing her beautiful baby to the world and not just a marathon winner lapping up the crowd’s appreciation. It looked to those watching that her victory had a meaning and a purpose she could never have imagined.

Yet Isla is no four-leaf clover, no talismanic lucky charm, and having her has not kept the freakish accidents and injuries at bay. Since her arrival, Paula has been forced to pull out of the London Marathon twice and the World Championships in Berlin this year, while she was way down the field at the Beijing Olympics. But New York came to the rescue again in 2008, restoring her faith in her body and her talents.

On Sunday Paula will go for New York victory No 4. She hasn’t been able to run a marathon in the intervening 12 months; New York is where she goes again to be saved. For all her calm demeanour and sunny disposition she has admitted the injuries and interruptions in the last year have been “wall-thumpingly” frustrating. This is Paula’s reality; what she has been trained to do, what she was born to do, keeps on frustrating her.

After this weekend the aim is to run in London in 2010, but it is always the plan to run London. The difference between Paula’s aims and her achievements is usually to do with physiology and never her guts and determination.

If she hadn’t sat down on a roadside in desperation at the Olympics in Athens in 2004, I wouldn’t need to suggest that we don’t appreciate her enough, or persuade you that she is possessed with extraordinary guts and determination. But this woman is a phenomenal marathon runner: five times she has smashed her own world record and of her first seven marathons, she won six.

No sports scientist worth his or her salt was surprised by what Paula’s body achieved less than a year after giving birth. We have seen it before in marathon runners. Liz McColgan, Ingrid Kristiansen and Lisa Ondieki all ran successfully after giving birth.

The old East German sports regime, which would try anything for a gold, allegedly forced some female athletes to get pregnant and then aborted the foetuses because the hormonal surge gave the athletes a huge increase in performance levels. I’m not condoning this: scientifically it may work, morally it’s bankrupt.

Scientists also agree that the physical benefits are short-lived. After a nine-month gestation period, for example, the increase in lung size that is often cited as a positive goes down almost immediately. Most mums would never get back to training quickly enough to gain an advantage.

But new mums will attest to looking back at the first few months of their baby’s life and wondering how they got through it. It’s one thing, though, showing up in the office and going through the motions of your job after a bad night, another to do a 12-mile run at speed.

What you cannot quantify with laboratory experiments is the motivation and inspiration a child can bring to a mother’s life. I feel sure that Kim Clijsters’s daughter, Jada, brought her mum back to tennis in a way that the promise of a trophy could not on its own. In that two-week period at Flushing Meadows in September, Clijsters was so at peace with herself that she could not fail. I do not believe Kim would have been competitive in New York if it hadn’t been for Jada and I am not sure Paula would still be running at the very top if it wasn’t for Isla.

In the Seventies my Auntie Jayne was nanny for a New York family, the Trotmans. In 1973, Suzy Trotman was driving from Manhattan to Long Island. In the back of the car her children, Nicky and Julia, were strapped in their seats. A lorry carrying oil crossed the central reservation and smashed into her car. Within minutes firefighters were on the scene. They helped Suzy to escape, but the back was burning with the oil seeping in at speed.

Suzy escaped the clutches of the firefighters holding her back and returned to the car. She somehow pulled her children from the burning wreck, losing most of her fingers in the process and breaking the children’s collarbones to get them out of their seats, displaying super-human powers. Julia went on to win a bronze medal in yachting at the Barcelona Games.

If the endgame for Paula is London 2012, when she’ll be 38, Isla will have to watch her mummy dig to depths even Paula didn’t know she had. Winning New York on Sunday is just the first step on a three-year journey towards that elusive Olympic medal. But if she can make it there ... well, you know the rest.

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• Graham Spiers