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Last weekend, sportsmen and women of an unusually hardy disposition descended on Sherborne, a pretty Dorset town. There, they swam twice around Sherborne Castle’s lake, cycled 180km and then ran a marathon. The winners of this gruelling race—Britain’s inaugural Ironman triathlon—were rewarded with a spot in a prestigious race in Hawaii, where yet more pain awaits.
For a sport barely known in Britain five years ago, triathlon has grown at a sprinter’s pace. This year the British Triathlon Association, the governing body, will sanction some 450 triathlons, duathlons (running and biking ) and aquathlons (running and swimming). These vary from tough races aimed at endurance junkies to shorter events designed to lure newcomers. By far the most successful is the London triathlon, which, three weeks ago, brought 8,000—half of them first-timers—to the Royal Victoria Dock in east London. That made it the world’s biggest.
There are echoes of the jogging craze of the early 1980s. Both sports are American exports; both have grown partly thanks to television coverage. Inclusion in the Olympic and Commonwealth games has conferred credibility and state funding on triathlon. Even better, Britain’s professional triathletes are doing rather well on the international circuit.
There are practical reasons for the growth of the sport, too. Nick Rusling, event director of the London triathlon, points out that established events such as the London marathon and Great North Run are hugely over-subscribed (this year the marathon received 98500 applications for 36000 places). Triathlon offers amore reliable route to exhaustion, and a fresh challenge to athletes who are likely to cross-train anyway.
The sport will not soon supplant "the great suburban Everest", as Chris Brasher, founder of the London marathon, described his event. The sport’s tripartite nature means that putting on events is fiendishly complex, a fact reflected in high entry fees: competitors at last weekend’s Ironman race forked out ￡ 220. Shorter events are cheaper, but participants must still provide their own bicycles and wetsuits and pay for training. Compared with the inhabitants of Newham, the London borough where this year’s London triathlon was held,competitors appeared overwhelmingly white and middle class.
Another drag on growth is a shortage of suitable venues in a small island—a problem exacerbated by safety fears. But that ought to be less of a hindrance in future. Two court decisions, in 2003 and earlier this year, have firmly established that the owners of large bodies of water may not be held responsible when adults injure themselves as a result of extravagant sporting actions.

The meaning of the word "gruelling" in the first paragraph is most close to（）