Tokyo Olympics 2020: Kiwi runner Zane Robertson can't remember end of gruelling marathon

Kiwi marathon runner Zane Robertson's amazing bid for an Olympic medal was so exhausting that he can't recall the last quarter of the race.

The 31-year-old has posted "the lights went out" at about the 32km mark in the 42km race.

Robertson and about 30 other runners tried to go toe-to-toe with the legendary Eliud Kipchoge before the Kenyan supremo blew the field apart in Sapporo, further boosting his reputation as probably the greatest marathon runner of all time.

Zane Robertson of New Zealand is helped into a wheelchair by medical staff after competing in the men's marathon at the Tokyo Olympics. Photo /Getty

The Olympic marathons were moved to Sapporo, 800km north of Tokyo, where the conditions were kinder than in the capital. But they were still harsh, with 79 per cent humidity and temperatures approaching 30C leading to a quarter of the 105-man field failing to finish.

Robertson was among the most affected, needing medical assistance and a wheelchair after batting across the finish line.

Zane Robertson lies on the ground after competing in the men's marathon at the Tokyo Olympics. Photo / Getty

"I left it all out there today, no excuses," Robertson posted on Instagram.

"I put myself in with a shot at a top 10 and perhaps a medal shot up to 30/31 km.

"My last memory (was) passing Desisa of Ethiopia before the lights went out around the 32km mark."

Robertson spent a large part of the race in the leading pack but finished in 36th position, about eight minutes behind Kipchoge.

Robertson won a 5000km bronze medal at the 2014 Commonwealth Games and competed on the track at Rio five years ago. Robertson and his twin brother Jake, who were born in Hamilton, live and train in Kenya.