They will need thighs of steel and a shed-load of determination to reach their goal.
But two friends from Wymondham are confident they will be able to run and cycle their way from Lands End to John O'Groats.
Mark Brown, 40, and Carl Bates, 49, hope to cover the breath of Great Britain in a series of seven runs about 30 miles each and seven 110 mile cycles over 17 days.
Mr Bates said their training had been going well around Norfolk's quiet country lanes, but the challenge itself would no doubt offer a few surprises.
He said: 'I think we will be in for quite a shock in places, such a Cornwall or the Lake District, as in August places like this will be incredibly busy. We have also had very few days where we have had to contend with the weather.
'Norfolk is also a relatively flat county and the hills will make a significant difference to our daily pace.'
But it is not just the thrill of achievement that has motivated the pair, who met at antenatal classes for their first children nearly 20 years ago.
Mr Brown and Mr Bates hope to raise up to £5,000 for two charities which are close to their hearts.
Mr Bates is fundraising for Parkinson's UK - he lost his father last year to the disease. He said: 'He battled Parkinson's for 15 years and passed away after suffering a fall, breaking a hip and never recovering.'
Mr Brown is raising money for Mind - the mental health charity which is important to him after he lost his step-father nearly 30 years ago.
He said their training had included cycling Peddars Way and Marriott's Way up and back, running the Milton Keynes Half Marathon, taking part in a 'Wolf Run' trail and obstacle run and doing several Eaton Park Parkruns.
Mr Brown said: 'The toughest things to overcome will be the aches and pains.
'Pushing on when you hit the wall and it all seems to much, eating correctly will be a massive thing and also the correct recovery as we only have a few hours really between starting and finishing each day.'
The pair plan to start what they are calling the 'Bonkers Tour' the tour on August 11.
Visit www.justgiving.com/fundraising/carl-bates2 and www.justgiving.com/fundraising/Mark-Brown87 to donate, and thebonkerstour.wordpress.com to follow the challenge
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