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The annual Beachy Head Marathon, which covers a challenging route through the South Downs National Park countryside, is taking place on Saturday.
New Covid safety management procedures will be in place, with the 1,500 runners setting off on the 26.2-mile route in staggered waves.
Social distancing measures include the introduction of a large holding area near the start line with distanced waiting pens, the wearing of mandatory face masks, and staggered times of arrival.
There will be a ban on overtaking on parts of the course, and volunteers will be wearing PPE.
Sealed plastic water bottles will also be provided on the course rather than water in paper cups.
Spectators are being discouraged from attending to help maintain social distancing and ensure the safety of those taking part.
The 10k marathon is being held on Sunday, while the half-marathon took place last weekend.
Runners in an array of colourful costumes take part in a virtual London Marathon across the country.
By Alice Evans
Rhys Jenkins became the fastest person to run around the coast of Wales - the equivalent of 33 marathons.
- Copyright: Brighton Marathon Weekend
The Brighton Marathon weekend, which was postponed in March and was due to take place between 18 and 20 September, will now not go ahead as planned, organisers say.
In a statement, marathon organisers said: "Not hosting the Brighton Marathon Weekend this September is not a decision that we have taken lightly."
They added that managing social distancing crowds would be "extremely difficult".
Although they are unable to shut down large parts of the city for the usual 26.2 mile course, organisers said they were working instead on creating a "socially-distanced, Covid-19 compliant event, which our 2020 participants will be invited to be part of" this autumn.
Further details of the revised event and options for registered runners will be released by mid-August.
- Copyright: Reuben Tabner
Organisers of the Loch Ness Marathon are still planning for the event to go ahead on 4 October.
But event director Malcolm Sutherland said he is waiting on further guidance from the Scottish government, World Health Organisation and other public bodies.
In the event it cannot go ahead, entrants will be offered a refund or a place in the 2021 edition.
The Covid-19 lockdown has led to the cancellation of races across the world, including September's Berlin Marathon and the Boston Marathon, which was last week called off for the first time since 1897.
The re-scheduled London Marathon is due to take place on the same day as the Loch Ness race.
But event director Hugh Brasher last month said he "cannot be certain" it will go ahead and pledged to give a further update on 21 June.
Runners are turning to virtual races to help their mental health while mass participation events are cancelled or postponed.
A Bristol primary school has smashed its £100 fundraising target and raised £1,510 for hospitals in a joint marathon between pupils.
Redfield Edge Primary School in Oldland Common, started the fundraiser after being inspired by pupil, Harvey Thomas, who asked his class if they would like to run a mile each to collectively achieve a marathon.
He said he wanted to do it after thinking about how hard his sister Sophie has been working for the NHS.
His mother, Sara Thomas, 45, said every child in the class has now taken part, including the teachers who "all put their heart in it" and added, some students "scootered, cycled, ran and one who is a gymnast even walked on their hands."
She said: "They're all doing it together but separately of course, which is important because they're a small school and have known each other for four years, so miss each other a lot."
The school's headteacher, Lisa Robinson, said the "community spirit" at the school has been "amazing".
She added: "I'm incredibly proud of all the children in Willow class and wish to thank the parents for their support in this."
RAF man swaps uniform for Star Wars Stormtrooper outfit whilst running 1,000 miles for charity.
By Steven McKenzie
BBC Scotland Highlands and Islands reporter