Training for a marathon and running 26.2 miles is hard work which is not made any easier because you have a well known name or a famous face.
Yet every year hundreds of celebrities take on the challenge to raise money for good causes or simply for a personal challenge.
As the Virgin Money London Marathon says #ThanksABillion to everyone who has helped to ensure this year's event on April 28 pushes total fundraising since 1981 past £1 billion, some famous faces share their tips for anyone tackling their first marathon.
Model and TV personality Nell McAndrew, 45, is one of the quickest female celebrities ever to have run the London Marathon with a personal best of two hours, 54 minutes and 39 seconds in 2012.
The mother-of two says this year she just wants to "go and enjoy it" regardless of her time.
"Just prepare as much as you can. If you get used to time on your legs, then you just want to be able to go and enjoy it.
"You don't want to be going and being in pain and suffering. "You want to just think 'right, I know what it feels like to run 20 miles, you know, and I know it's going to be tough'.
"But if you just go steady, at your own pace, let everybody else go their pace and just smile.
"Save a big smile and a little bit of a sprint finish if you can."
David Weir won a record eighth London Marathon title in 2018 and hopes for more success this year when he takes part in his favourite race for the 20th time.
"Make sure you get all your training runs in. Make sure you eat the right foods. Make sure you do a biggish one before, a big run to make sure you can cope, maybe like an 18 to 20 miler.
"And then on the day, or even the week leading up, make sure you carb up, you know, lots of early nights, no alcohol, lots of fluid, electrolytes and just enjoy it to be honest, you know, just enjoy your first ever marathon, cos it's truly amazing."
London Marathon event director Hugh Brasher is the son of Chris Brasher who co-founded the London Marathon in 1981 when 7,747 runners took part. Last year 40,272 people finished the race.
"My one tip if this is your first ever Virgin Money London Marathon is put your name on your T-shirt or your vest or whatever it is that you're going to be wearing.
"Because what is unique about this event is you will have tens of thousands of people on the day of the event cheering your name, wanting you to be successful and that is a feeling that you will never get probably for the rest of your life unless you do the marathon again.
"Because we don't play at Wembley Stadium, we don't play at the Centre Court of Wimbledon, we don't have people chanting our name.
"But on that one day you will have tens of thousands of people wanting you to get to the finish line, wanting you to get to The Mall, raise money for charity and it will be something that you will remember.
"So put that name on your T-shirt, put it on your vest, whatever it is and I promise you it will make that day even more special."
Dame Barbara Windsor's husband Scott Mitchell, who is training for his first marathon, also offered some words of support for anyone finding it hard. "When my legs are tired and when I want to give up and when I think 'why am I doing this?' I remember why I'm doing it.
"And usually I think people that are running, if they're not professional athletes, they are doing it for a cause.
"And that's what keeps you going, keep either that person or that campaign or charity in focus.
"That's how I get through it."
Mitchell and some of his wife's EastEnders co-stars are running the Virgin Money London Marathon as Barbara's Revolutionaries, raising money for Dementia Revolution, a partnership between Alzheimer's Society and Alzheimer's Research UK which is the event's charity of the year. Dame Barbara was diagnosed with Alzheimer's disease in 2014.