Tens of thousands of people are expected in Cardiff for a gruelling fitness challenge to be held over three days at the Principality Stadium.
Hyrox is a "fitness racing" event that has become a craze, going viral on social media since the first competition in Germany eight years ago.
There are now 200,000 competitors worldwide according to organisers, with the first ever event in Wales starting on Friday.
The event is set to include the oldest known participant in the gruelling indoor race of eight 1km (0.62 mile) runs followed by different fitness exercises.
"Age doesn't have to be a barrier," said Prof Peter Herbert, 80, from Carmarthen. "Vitality is something we can choose to nurture every day."
As the Hyrox craze descends on the capital, roads in the town centre are expected to be busy until after the final on Sunday.
Competitors – either professional or everyday fitness enthusiasts – perform eight runs and eight workouts, including 1km on a standing ski machine, 50m sled push and 80m burpee jumps.
Economist Dylan Jones Evans previously said "tens of thousands" could visit the Welsh capital to take part in the event.
"What we saw with Hyrox when they went to Glasgow recently was 40,000 people going to the city who wouldn't have gone to Glasgow," he said.
