You can follow Jamie's progress on twitter @MrJamieMcDonald or at http://www.facebook.com/jamiemcdonald.org
Jamie will be running across Canada during part of their winter, so will encounter Arctic temperatures he has never experienced before.
We took him to Gloucerstershire University's Sport & Exercise Laboratory where they have a chamber in which the temperature can be lowered to minus 20C.
Jamie McDonald has already cycled 14,000 miles from Bangkok to his home city of Gloucester. Just two weeks later he spent 265 hours on a static bicycle; the world record is 224 hours.
As if that wasn't enough, he has a new project... He plans to run across Canada, coast to coast.
The distance is more than 5,000 miles. It is the equivalent of running 200 marathons, and he will do it all in 275 days.
Jamie suffers from a rare condition called Syringomyelia, when cysts or cavities form in the spine.
It meant he was in and out of hospital for most of his childhood. He now wants to raise money for the hospitals that helped him - Gloucestershire Royal's Pied Piper appeal and Great Ormond Street.