The gruelling injuries Nedd Brockmann endured for 1600km charity ...

Feet so swollen and blistered that his shoes no longer fit, but he kept running. Surviving on about two hours sleep and using elastic bands to lift his feet when they failed him, but he kept running. Bleeding from working up such a sweat and being put in a wheelchair to get around. But he kept running or, by that point, limping to the finish line.

That's what Australian ultramarathon runner Nedd Brockmann endured to reach his goal of doing a 1600-kilometre run over 10 days in Sydney.

He ultimately didn't beat Greek ultra runner Yiannis Kourous' 1988 world record, instead spending 12-and-a-half-days getting the gruelling challenge done, but nevertheless, he raised more than A$2.5 million (NZ$2.75m) for a non-profit homelessness service, We Are Mobilise.

"Get comfortable being uncomfortable" - that's the 25-year-old's motto which prepared him to sacrifice his body to achieve this feat as well as many others across the years. The former electrician turned endurance athlete became well known in 2022 when he ran 4000km across Australia in 46 days, raising A$1.85m to charity.

Live streamed on TikTok as "Nedd Brockmann's Uncomfortable Challenge", he finally crossed the finish line on Wednesday morning to jubliant cheers from dozens of supporters, the ABC reported.

He's finally able to put his feet up after running for about 16 to 20 hours a day, lapping up about 160km daily, around the 400-metre athletics track at Sydney Olympic Park.

On day 10, he told his Instagram followers he expected injuries to flare up, but never could have imagined it would be this bad.

"As humans, I believe it is our duty to see things through. This 1000 miles around that track has been the most humbling experience of my life. Never have I ever felt so many emotions to the absolute peak of them all.

"My toes were like King charles' fingers after day one. I've had no function of my right ant tib [anterior tibial tendon] since the end of day three, so I've been snapping dictus band rubbers left right and centre. No sleep because the tendinitis everywhere punches me in the throat come rest time. The feet have swollen three sizes due to the rain/track. It's healthy stuff."

He also thanked his supporters and those who donated.

Brockmann also endured terrible weather when a severe thunderstorm hit Sydney earlier this week, the Sydney Morning Herald reported. His injuried were so bad he had to be taken back to the course in a wheelchair each morning.

He was already going into the run with an injured left shin, and the right one started hurting on day three. He had to put on a moon boot, with his foot unable to be flexed. "It was so overused it was just dangling with stabbing pain," the Sydney Morning Herald reported Brockmann saying.

"I'm quite new [to running] so the price I have to pay is the injuries," he said. "I'm so relieved right now, my brain is at ease."

His physiotherapist, Alex Bell, told ABC's Sport Daily that on day three the runner's shoes had gone up about three sizes.

"He started in a 9.5, we're now in a 12, the feet are pretty swollen ... I can tell you that this morning we just made some modifications to that shoe as well, where we've cut the upper of the shoe and just tried to clear a little bit more space."

Team leader James Ward told ABC News that Brockmann was feeling relieved after completing his mission, but he felt like he was racing against the clock every minute, even when he needed to use the toilet. He was also eating and sleeping at the athletes' centre near the track.

"He wasn't confident, until 800 metres to go, that he was going to make it.

"He's the second fastest Australian to run the 1000 miles, he's the 10th fastest in the world, and looking at the numbers, I think, he's the youngest person in that top 10 by, on average, around 20 years.

"This is his uncomfortable challenge and ... you'll absolutely see that this man is putting his body on the line, enduring like no other human I've seen, you know, really challenging what I thought was possible from a phsyiotherapy sense in terms of how much pain someone can actually endure."

Among the celebrities who turned up to show support for Brockmann was New Zealand UFC fighter Israel Adesanya, who posted a series of pictures on his social media account, showing the pair on the track.

"On the kilometers I did with Nedd, we just learned about life, pain, joy, love, family, good friends…etc. But for me, the main gem was feeling a small fraction of what Nedd's done and realizing I have zero right to even complain due to what this man has put his body through to bring attention and funds to this problem," he wrote on Instagram.

Adsenya previously expressed admiration for Brockmann's efforts to raise money for charity in 2022, which moved the young runner to tears.