When Steve Pontifex completes a marathon across the desiccated wilderness of Chile's Atacama Desert next week, the aches of his muscles will be offset by the knowledge that four children born with facial deformities will be on their way to having normal lives.
That gratification will be helpful because the morning after running that marathon, he will run another. Then another and another, until finally he will have covered 250 kilometres over the course of a week.
Over the next three years, he aims to repeat that feat three more times, completing similarly gruelling ultra-marathons across the Sahara and Gobi deserts before finally taking on the frozen wastelands of Antarctica. For 1,000km of pain and deprivation in some of the planet's most inhospitable environments, the payback will be having raised enough money for the UAE-based Operation Smile charity to fund 100 facial reconstructions for underprivileged children born with cleft palates.
"For every Dh880 I can raise, a child gets a new life, to make them what we call normal," he says.
"I think about it every time I look at my two-year-old daughter and see her perfect smile. That's so uplifting and you think of a parent who looks at their own child and they don't get the same joy."
The four-deserts race series is rated as one of the world's toughest endurance events and Pontifex, an air-traffic controller from Australia, is expecting it to be a significant step up on anything he has done before.
And it's not like he's a couch potato. He has completed 10 Ironman races, each one an event deemed beyond the abilities of most athletes.
"I've been doing the Ironman for a while then I came over here three and a half years ago," he adds.
"I was doing these races and the only person getting a benefit was me, so I decided it was time to give something back.
"I saw a list of the top 10 endurance races in the world and the four-deserts series was on it."
Having found his challenge, he started looking for a charity for which he could raise money.
"I was looking for a charity in the UAE. I'm getting paid here and all my money is tax free here so I thought I might as well support something based here," he says.
Operation Smile met his checklist of a local, transparent and useful organisation, so he started seeking donations.
After doing the Yas triathlon and then an Australian Ironman event for the charity, he signed up for the Atacama Crossing in Chile as the first of his four desert races.
His aim is to raise Dh100 for each kilometre he races. So far, he is ahead of the curve, having raised a little more than Dh28,000 - enough for more than 30 facial-reconstruction operations.
Part of this is his own vow to match the cost of competing in each race with a donation to Operation Smile, so for every dirham that he spends he gives a dirham to the charity.
Now he just has to complete a 250km endurance race through the driest desert on earth, starting on March 3, living for a week almost entirely on what he carries on his back.
"You've got to take everything for five days with you. They provide tents for eight to 10 people to sleep in and they'll supply you with water every 10km," he says.
"You have to have your sleeping bag, medical kit, clothes. We've managed to whittle it down to just under 10 kilograms, without water.
"My luxury items are a camera, a toothbrush and earplugs. Those are my only luxuries. Everything else is mandatory equipment.
"A 10kg pack slows you down by about half an hour over 10km. You look at some of the times to do 42km and some people are taking nine hours. It's the sand and the altitude that slows people down.
"They reckon the temperatures get between 10°C and 30°C, and you might get up to 40°C, but that isn't a big problem because I've been training in Abu Dhabi. I'm used to running in the middle of the day because of my shifts.
"I live at Al Reef. I can take out from my back door and in 10 minutes I'm in sand dunes."
But while Abu Dhabi is an ideal place to train for a hot race through an occasional desert, he has been unable to prepare for the thin air at altitude. The race is set an average of 2,500 metres above sea level and exceeds 3,000m on the first day.
"With the altitude, there's nothing I can do. I have three days of acclimatisation before the race begins," he says. "The first day is a straight 42km across all sorts of terrain - rivers, salt flats, across rocky mountains and up and down dunes.
"You do a marathon and then you have to get up again the next day and do it again. When you wake up and you know you have to do 42km, you think, 'why am I doing this? I'm never doing this again'. It wears you down mentally."
But his Ironman training has prepared him for that process.
"There are stages on Ironman races where your mind is trying to make you pull out or stop.
"For my first Ironman, I ran across the finish line and said I was never going to do that again. Three hours later I was signing up for the next year.
"But it's amazing what your body can get used to. For my training, I've tried to do big runs back to back, 20km then 20km."
Pontifex chose to do the Atacama Crossing first almost by accident because it was the first one listed on the race organiser's website.
One major motivator is knowing that every time he reaches one of the regular water stations, he will have raised enough to pay for one of Operation Smile's facial reconstructions.
His next race will be the Gobi March in western China. The terrain - sand dunes, rocky trails, steep hills, ridges and riverbeds - is inhospitable but it is the strong winds in the area that are notorious for tormenting runners.
The Sahara Race in Egypt is the hottest of the four races and mostly based on loose sand. Then there is the Antarctic leg, the fourth in the series, in the summer of 2015.
"They all have their own challenges. Antarctica will be the coldest," Pontifex says.
"You can't do it until you've done two of the others. You'll have to have so much gear in Antarctica. Just running in my thermals doesn't appeal too much."
He is already looking beyond the four desert races, thinking about a mammoth endurance event closer to home to raise money and awareness for Operation Smile.
"I'm looking for a big event in the UAE," he adds. "Maybe running from the Saudi border to Ras Al Khaimah or something ridiculous like that."