But oil rig geologist Dan Walding has already run a marathon in Tokyo and is training for another in New York later this year.

When he's stuck on oil rigs in Russia and Greenland, the Lorne resident sometimes keeps fit by running laps of the helipad. He is presently preparing to run in The Sunday Age City2Sea, presented by Westpac.

Working four weeks on and four weeks off in different far-flung locations, it's easy to lose the motivation to stay healthy. Particularly when it's so tempting after a hard day's work to do nothing.

"Usually the rigs have got really good food and awesome dessert fridges," the 41-year-old said. "You work 12 hours a day; it's really easy to get lazy. Most guys on the rig are fairly large and unfit."

When they do work out, Dan's colleagues tend to lift weights in the gym, avoiding cardio workouts. That leaves the treadmill for Dan. If it's broken, he'll head outside and run laps.

"Safety first is drummed into us on the rig, but it is 28 metres down. You don't really want to fall off," he said. "Generally you're just doing laps. You can only really jog. It's a good way of keeping fit; you've got to have routine on the rig." 

Dan said he originally took up running on the rig as a way of staying slim, but then found he enjoyed it.

He likes taking part in fun runs and marathon and uses them as motivation to make sure he keeps training.

Preparing for marathons has been a particularly difficult challenge, something he found while running the 42-kilometre course in Tokyo.

"I got to 31 kilometres and it was like all the colour got sucked out of the world. It felt like I was looking at the telescope the wrong way round," he said.

Hopefully that doesn't happen during the 15-kilometre City2Sea event, which Dan is looking forward to competing in.

"Keeping fit, it's great to have these targets," he said.

Entries are open now, visit thecity2sea.com.au