A 2.4-mile (3.8km) open-water swim before 112-miles (180km) on the bike and a 26.2-mile (42.2km) marathon run. Or the equivalent of swimming from London Bridge to Big Ben in the Thames, cycling to Bristol and then running down to Glastonbury. In less than 17 hours. There’s a reason an Ironman triathlon is seen as the ultimate one-day endurance sport challenge.
And it was an ultimate Ironman challenge in Kona that former racing driver Billy Monger took on for Comic Relief 2025, completing the 2024 Ironman World Championship event in a record time for a double-leg amputee by crossing the hallowed Ali’i Drive finishing line in 14 hours.
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Ironman is the major organiser of these long-distance triathlons around the world (and holds the copyright to the name), but there are many other race organisers offering Iron-distance events, some that offer courses for beginners to Iron-distance racing (see the UK Ultimate Triathlon and Outlaw in the UK) and others at the extreme end of Iron racing.
There are also a wealth of shorter triathlons for athletes to enter, including sprint, Olympic, middle-distance/Ironman 70.3, as well as off-road triathlons, run/bike/run duathlons, swimrun, aquathlons, aquabikes and more.
When did modern-day triathlon?
Modern-day triathlon began in San Diego in 1974 after a debate between single-discipline athletes about whether swimming or running was the toughest sport. The first Ironman Hawaii was held in 1978 and it’s still the sport’s flagship race, the Big Island of Kona becoming the Wembley, Wimbledon and Lords of triathlon.
What are the triathlon distances?
These are the standardised distances in kilometres (the usual metric for listing race distances), but there can be differences at each event:
- Super-sprint-distance – 400m swim/10km bike/2.5km run
- Sprint-distance – 750m swim/20km bike/5km run
- Standard/Olympic-distance – 1.5km swim/40km bike/10km run
- Middle/Ironman 70.3 distance – 1.9km swim/90km bike/21.1km run
- Ironman – 3.8km swim/180km bike/42.2km run
