Celebrities including Stephen Fry, Ellie Goulding, Ross Kemp, Gareth Bale and Davina McCall are supporting a campaign to help UK charities who are facing a shortfall in their budgets.
The 2.6 Challenge officially starts on Sunday – the day the London Marathon was due to take place – and involves participants completing a task based around the numbers 2.6 or 26.
More than £1.5 million has already been raised by the campaign.
Fry has previously posted a video on social media of him attempting to use a cricket bat to hit a ball up in the air 26 times in a row.
He said he would auction the bat, which is signed by members of the England cricket team, in support of the Ruth Strauss Foundation.
BBC sports commentator Clare Balding has also taken part in the challenge, getting her dog Archie to give her 26 high fives.
The campaign is being supported by a host of other sports stars and celebrities.
Hugh Brasher, event director of London Marathon Events and co-chairman of the Mass Participation Sports Organisers group, who created the challenge, said: “For many of the UK’s charities, the day of the London Marathon is the biggest fundraising day of the year.
“One of the founding pillars of the London Marathon was ‘to show how the family of mankind can be united’.
“We hope that the 2.6 Challenge, which starts on the day our 40th race should have taken place, will embody that spirit and inspire people families and communities to fundraise for their chosen charity to help save the UK’s charities.
“Right now, our vulnerable members of society need the help of charities more than ever before.
“We are asking everyone to create a 2.6 Challenge of their own and raise funds or pledge a donation.”