Most social joggers know what it feels like mentally and physically after they hit what is known as "the wall".
It is a very uncomfortable feeling, as your body is screaming at you to give it a rest, and a dull, blankness invades your conscious mind as you keep putting one foot after another.
Well, imagine doing that for more than eight hours around Hagley Park in Christchurch in the NZ 100k National Championships - which is what Tauranga runner Russell Lake did last weekend in a superb performance to claim his first national title.
It was the first time the 43-year-old had entered the full 100km distance and he won the event in 8:08.52 - nearly 51 minutes ahead of second placed David Ryan from Wellington, who is 28.
It was the third fastest winning time in the iconic event since the slick time set by Seaton Meredith in 2006 of 8:03.34.
Lake is a multiple winner of the Tarawera Ultramarathon, which is run over 85km, but the course is an extreme off-road challenge compared to the flat terrain of Hagley Park.
But it was no mean feat for Lake to win the 100km race by such a staggering margin.
"There is not much chance to rest and I was worried before the race that it might get a bit boring," he said.
"But in some ways it was good having multiple laps because you could constantly go past the food and drinks stations, and keep looking after yourself. I had a mixture of energy gels, and chia seeds mixed with water to provide a natural form of protein and electrolytes, plus a sandwich with extra Vegemite and raspberry jam in it. It works for me!"
He says the biggest difference with stretching out to compete at 100km distance is the pace.
"In a marathon you need to go pretty hard and run at that limit for as long as you can, where as the 100k you have to back off the pace and be a bit more sensible, and really look after yourself a whole lot more.
"Mentally it is tough. There were plenty of times my body was saying stop, just walk, so the hardest thing is to just keep on going and force yourself to get running again after picking up the food and drink.
"The hardest part was about 65 to 90ks when I had a good lead. I got passed at the 20km mark when I sat down to deal with a blister and it took 30km to catch up with them and get the lead."
Lake has an impressive racing career with numerous placings at national Masters age grade events and last year at the Oceania Master Games, held in Tauranga, he won his age groups in the 5000m on the track, the 8km cross country and the Half Marathon.
"Winning the 100k feels good and is the culmination of winning the Tarawera Ultra 85k by about 20 minutes and winning the Length of the Lake in Taupo in a course record by 18 minutes. I also set a marathon PB in Auckland last October so I am getting faster as I get older."