This year's Cardiff Half Marathon, is the biggest event yet, with 25,000 runners taking part. A number of them are hoping to break records.
This time last year Brian Thomas was recovering from critical injuries after collapsing while walking near his home in west Wales.
After spending four weeks in a coma, he was told by doctors that he would remain in hospital for more than a year and that it could take up to five years for him to fully recover from his injuries.
Today, he took part in the Cardiff Half Marathon, to raise money for the A & E unit of Withybush Hospital, who helped him after his collapse.
Doctors said it would take five years for Brian Thomas to get better, but a year and a bit later he is running the Cardiff Half Marathon.
An announcement about this year's Cardiff half-marathon is expected later.