From 5K to Ironman: the guide to race formats (so you never mix up swimrun and ekiden again)

In short From the 5K to the Spartathlon, via trail, triathlon and ekiden, every race has its distance, its crowd and its traditions: here's what you need to find your way.

5K and 10K: the gateways

The 5K is the ideal distance for a first race: within reach after a few weeks of training, long enough to taste a real race. For experienced runners, it's a speed event: it's short, and that's exactly why it hurts from the first metre to the last.

The 10K is a road-race classic, often in town. A first real goal for many, a record-hunting ground for others. Long enough to be a proper race, short enough to be home before brunch.

Who it's for: beginners, and anyone who wants to work on speed.

The half marathon: 21.0975 km, not a metre less

Exactly half a marathon. A true endurance distance that needs serious preparation but stays manageable. Often a step towards the marathon, sometimes a goal in itself.

Who it's for: regular runners who want a long challenge without jumping straight into a marathon.

And no, the 97.5 metres after the 21st kilometre are not negotiable. Anyway, nobody says "I ran 21.0975 km": you say "I did a half", and that's enough to impress the family.

The marathon: 42.195 km and a legend

Legend has it that after the battle of Marathon, in 490 BC, a Greek messenger ran to Athens, about forty kilometres, to announce victory over the Persians, before collapsing. A nice story, but take it as a legend: it only appears in much later writers. Herodotus, the great historian of those wars, tells of a different run (more on that with the ultra).

The marathon as we know it was born at the first modern Olympic Games, in Athens in 1896, on an idea from French linguist Michel Bréal. But its distance varied from one edition to the next. The famous 42.195 km come from the 1908 London Games: the course started at Windsor Castle and finished in front of the royal box in the Olympic stadium. The distance became official in 1921. If the last 195 metres feel like too much, you now know who to blame.

Who it's for: those ready for several months of preparation. The marathon has its own folklore, like "the wall", the dreaded slump that often lurks around the 30th kilometre.

The ultra: when 42 km isn't enough

Any race longer than a marathon is an ultra: 50 km, 100 km, 6, 12 or 24-hour races (you loop a circuit and count the kilometres), multi-day events.

One of the most legendary is the Spartathlon, about 246 km from Athens to Sparta. It's inspired by Herodotus's account: the messenger Pheidippides, sent from Athens to Sparta to ask for help against the Persians. At the finish, tradition says you touch the foot of the statue of King Leonidas.

Who it's for: experienced, patient runners who like eating on the move. Past a certain distance, the race becomes a moving picnic, and the real question is no longer "what pace?" but "what's at the next aid station?".

Trail: the distance, plus the elevation gain

Trail running means racing in nature, on paths and tracks, often in mountains or forests. A trail race is described with two numbers: the distance and the elevation gain, the "D+" in French, meaning all the climbing added up. 20 km with 1,500 m of climbing has nothing to do with 20 km on the road.

To compare, trail runners talk about "effort kilometres": you add one kilometre to the distance for every 100 m of climbing. Those 20 km are therefore worth 35 effort-km. At the very top of the scale, the UTMB circles Mont Blanc through France, Italy and Switzerland: about 170 km and 10,000 m of climbing.

Who it's for: nature lovers, from short local trails to ultra-trails. Here, walking uphill is a respected strategy, and the view is an official excuse to stop.

Triathlon: three sports, one clock

Swim, bike, run, in that order, with the clock still ticking during transitions. The formats:

• XS, the taster format: shorter distances, perfect to try it out;
• S, or sprint: 750 m swim, 20 km bike, 5 km run;
• M, or Olympic: 1.5 km, 40 km, 10 km, the Olympic distance;
• L: 1.9 km, 90 km, 21.1 km, nicknamed "70.3", the total of the three distances in miles;
• XL: 3.8 km, 180 km, 42.195 km, the format often called "Ironman".

Who it's for: all-rounders, and anyone whose bike is gathering dust in the garage. Triathlon has an unofficial fourth discipline: transition, where you discover that pulling socks onto wet feet is a sport in itself.

Duathlon: triathlon on dry land

Run, bike, run: the triathlon idea without the swim.

Who it's for: those who want to try the switches without getting wet. Ideal if your relationship with water stops at your bottle. The second run, on legs fresh off the bike, leaves memories.

Swimrun: swim in shoes, run in a wetsuit

You alternate swim and run sections several times without changing: you swim in your shoes and run in your wetsuit. Born in Sweden, in the Stockholm archipelago, it's often raced in teams of two.

Who it's for: adventurers comfortable in open water (a requirement, not an option). The only sport where running in a neoprene wetsuit isn't a changing-room mistake.

Ekiden: the marathon for six

A marathon relay for six runners: 5 km, 10 km, 5 km, 10 km, 5 km and 7.195 km, 42.195 km in total. Born in Japan, where the relay is traditionally passed on with a sash, the tasuki.

Who it's for: clubs, colleagues, groups of friends. Guaranteed argument over who gets the 7.195 km: too long to be a formality, too short to brag about.

Cross-country: mud included

A race over natural ground (grass, earth, mud), often on loops, during the autumn and winter season. A great athletics club tradition.

Who it's for: club runners, and anyone who wants a livelier winter. At a cross-country race you don't come home dirty: you come home with a souvenir of the course on each calf.

Obstacle races

A race studded with obstacles: walls to climb, nets, crawling sections, mud pits, loads to carry.

Who it's for: from groups of friends out for fun to very sharp competitors. Your legs run, your arms climb, and your T-shirt will never be quite white again.

The recap

Whatever the distance, from 5K to Spartathlon, there's a calf to rent. And in an ekiden, that's twelve calves for a single team.