Eighteen months ago, John Mergler casually asked his fiancee, Debi Hazelden, if she was up for a bit of a challenge.
"I said, 'Debi, do you fancy doing 100 ironmen in 100 days?' " recalls Mergler, whose inspiration came from the "iron cowboy" who was doing 50 ironmen in 50 days across 50 states.
"She said 'Yes', so we started planning."
While most of us have broken a sweat during the record heatwave without moving a muscle, the couple have been battling their way through the stifling heat, attempting a world record with their "iron century".
"The first week was an average of 35 degrees throughout the day – that was a real challenge," says Mergler, a veteran ultramarathon runner who has competed in more than 60 ironman races (that's a 3.86-kilometre swim, a 180.25-kilometre cycle ride and a marathon 42.20-kilometre run).
Hazelden, a triathlon coach who has also competed in ironman races and ultras, was dealing with more than the heat.
She initially thought she had heat rash from the first two days of their challenge, both of which were 38 degrees.
The mum to 7½-month-old son Ryder, soon discovered that it was hand, foot and mouth disease, a common viral infection experienced by children and parents. While it made her "really uncomfortable", it was not enough to stop her from the commitment to 100 half-ironman races in 100 days.
"Now, I'm like 'Woohoo. It can only get better from here'," she says perkily.
Crook mum and bub aside, by day 13 of the challenge they had already had "everything thrown at us".
As well as the heat, they have experienced "torrential rain", Mergler strained an adductor tendon requiring him to delay his completion date by two days, they struggled with the monotony of going "round and round and round" Centennial Park, where they complete the run and cycle legs (they have a dedicated lane at Prince Alfred pool) and, having a sick son has meant that getting enough sleep has also been a challenge.
Of course, their bodies are also feeling it.
"Your legs are getting so heavy – it's battling that level of discomfort [constantly]," Mergler explains. "I use a head-to-toe scanning technique: make sure everything is working and analyse each part. Focus on technique; whether I need to stop for 10 minutes; am not hydrated enough."
He also distracts with music, podcasts and company, when people join him for legs of the race each day.
"Because there's been a bit of publicity, [people] are just joining in and wanting to do a couple of laps," the 57-year-old says. "At one point a dozen people were running with me last week ... and my brother joined me for 110 kays on the bike last week."
He hopes more people will get involved, saying the company distracts them from the physical discomfort.
"It would be nice to have 50 or 60 people join in – I typically get on the run about 5,6,7pm."
Mergler adds that, when he is on his own, it is as much a battle of the mind as it is the body.
"Your emotions can take control of your intellect – if you get a whiff of your own personal negativity, thinking 'It's all too hard' or 'I wish I was at home in front of the TV eating ice-cream' ... Intellectual rigour has to be introduced," he says.
Hazelden, whose parents are over from New Zealand helping to care for Ryder, also finds comfort in company, when people join in for a lap or six; and tries to keep her mind tethered to her technique.
"I really focus on my form – especially when your muscles are tired," the 36-year-old says. "I do listen to music as well – Ministry of Sound – on a little MP3 player."
Their goal to raise $100,000 for the Red Cross (they've raised $16,000 so far) is also motivation to keep going.
But mainly, they're doing it for fun.
Hazelden admits that "most strangers are like 'Oh my god, this is nuts'," but not anyone who knows the pair.
"Our family are used it it ... when we told them, they were like 'Oh OK'."
A DAY IN THE LIFE OF AN IRON CENTURY
The couple started their challenge on the January 28 and aim to finish in early May.
"Every morning we wake up at 5 o'clock and eat a little bit of breakfast – a strong cup of coffee and a bircher muesli we've made – and are out the door by 5.30," Mergler says.
"We have a dedicated lane at Prince Alfred pool. Hazelden takes about 35 minutes swimming, I take an hour and 10 minutes on average."
The pair then shower, drink a protein shake and are driven to Centennial Park, where they have another cup of coffee and do about 90 kilometres together on the bikes.
"I continue for another 48 laps then 12 laps running of Centennial Park, while Debi does six," says Mergler.
They take brief food and hydration breaks ("mates bake us little cakes – nice little snacks", and sports nutrition supplements) until Hazelden finishes each day at about 3pm while Mergler finishes about 7pm.
They then return to their nearby home, where dinner is delivered and provided by their sponsor, Foodora.
The couple spend some "cuddle" time with Ryder, get massages and go to bed, ready to do it all over again in the morning.