Of all the things I expected to experience on this sunny day of finely tuned fitness, the last was terror. But face-down in murky water, gasping for breath (which came with mouthfuls of water), I discovered it is possible to hyperventilate yourself into a state of complete panic within five minutes.
So I decided to stop. I didn't care that I had trained for this for six months, I had to get out of there. At which point I realised there was no way out; I had started off near the front, so if I slowed down, there were at least 250 women left to swim over the top of me. Life-or-death sporting moments tend to occur in dramatic circumstances; I was having mine surrounded by bunting and giant inflatable bottles of Michelob beer.
Having found my "inner strength", or whatever the term is for having absolutely no other options, I put my face back in the water, breathed less, and carried on. Three hours later I had finished the bike and run sections and was sprinting over the finish line, euphoric. Would I do it again? Yes (particularly as the swimming lanes will be wider this year, so the fish-farm effect should not last so long).
Triathlons were invented in San Diego in the early Seventies by a group of surfers getting together for a bit of fun. By the end of the decade, some friends in Hawaii had come up with even more of a wheeze: the Ironman, designed to work out who were the fittest - swimmers, cyclists or runners - via a 2.4-mile swim, 112-mile bike ride and a marathon. (The winner, Gordon Haller, regularly spent 10 hours a day doing all three disciplines, so the question about fitness was never answered.)
Triathlons are a more comfortable option. The Olympic distance (1.5km swim, 40km bike, 10km run) takes an average of three hours, though the quickest time recorded, by Britain's Simon Lessing, is 1hr 39min 50sec, and the Sprint distance (750m swim, 20km bike, 5km run) just over half that time.
Last year I was one of 3,000 first-timers in the London event, and the sport is currently growing at a faster rate than any other in the UK. The London Triathlon has become the biggest in the world (8,000 entrants are expected this year).
"The thing about triathlons is that almost anyone can do them," says Glenn Cook, two times European champion, six times British champion, and now a coach. "People like getting out of the gym, and the fact you're doing three sports means it's never boring. There are also fewer negatives in terms of impact on your joints than marathons."
The sport works for most sizes and shapes. Swimmers, cyclists and runners tend to have very different body-types, but the only thing you can guarantee of a hybrid of all three is that it will be "ripped and toned," says Cook. As all three disciplines are cardiovascular and burn fat, it's virtually impossible not to lose weight; I lost 10lb without trying. I did work out before, but not as much. However, knowing I had a three-hour race coming up kept me running or swimming long after I would normally have stopped.
If you're a beginner, it's up to you how seriously you take it. You can buy lots of kit and make a science out of how many carbs you eat, but competing in a triathlon can be very simple. "If you start now and do one swim, bike and run a week, working up to competition distances, you'll be ready by August," says Cook. More sessions a week would be even better, but you don't need to train for hours and hours.
Richard Stannard, one of Britain's best triathletes, advises: "Mix distance sessions with interval training. For distance sessions, aim for the average times for each of your disciplines [in the Olympic distance, this is 35 minutes for the swim, 90 minutes for the bike ride, and 50 minutes for the run], and for interval sessions, alter pace. At beginner level it really doesn't matter how you structure intervals - in time or distance - as long as you alternate between a fast and a slower pace."
Good running trainers are a must (get fitted out at a shop which watches you run), and you can shave off minutes with made-to-measure wetsuits and tri-bikes. "But you don't need a race bike," says Stannard, "people use mountain bikes and shoppers. A racing bike will go 20 per cent faster than a mountain bike, though, and using clip-on pedals makes the ride 20 per cent easier again."
Which sounds a lot - but you could save the same time by doing a faster "transition". I took at least five minutes on each one, putting my hair up and popping to the loo, whereas pros are out of their wetsuits or off their bikes and on to the next phase within 15 seconds.
If it appeals, "joining a club for all or any of the three disciplines is a great idea," says Stannard. "Training with other people really pushes you on."
But whatever else you do, book now. Entries close by 28 February (although after that it might still be possible to enter via various nominated charities).
For more information on the Michelob Ultra London Triathlon or Blenheim Triathlon: www.thelondontriathlon.com, or call 020 7559 2929 for an entry form.Reuse content