Over 42 nations will be represented at the World 24 Hour Championships which are being held in Victoria Park in Belfast on Saturday and Sunday.
Defending champion Florian Reus from Germany took the title with 263.9 kilometres last time and has been building up for the event where he could go close to the World record.
Pete Kostelnick from USA holds the Coast To Coast record in the States and like Aleksandr Sorokin from Lithuania has been beyond 260 kilometres.
Great Britain are the team champions and will be led by European champion Dan Lawson, known as ‘Dan The Running Man’ and Robbie Britton the bronze medallist in Turin last time.
National champion Eoin Keith heads the Irish. He has just broken the record for running the length of Ireland from Mizen to Malin. He is joined by Eddie Gallen who has flown in from his home in Madrid.
Patrycja Bornowska from Poland broke the World record in February. She will battle with Maria Jansson of Sweden.
USA look particularly strong with Katalin Nagy and Traci Falbo the top two in the last Worlds and new National record holder Courtney Dauwalter.
Cork girl Ruthann Sheahan, seventh in the 2012 Worlds, leads the Irish side.
USA have the biggest overall squad with 69 members.
The event starts at noon today and finishes at the same time tomorrow.
Leon Reid will hopefully get the Commonwealth 200 metres standard of 20.77 when he competes in the British Championships in Birmingham. The double Northern Ireland champion has already run 20.79 and 20.81 this season.
Mollie Courtney already qualified will be in the 100 hurdles along with Megan Marrs with Hayley Murray who threw a record 59.49 hammer at the Mary Peters will hope to beat the 60 metres barrier.
Young athletes will take centre stage at the Mary Peters Track today with the finals of the YDL League. The first event is at 10.15.