Encased in rubber and with two smiley faces inked on my hands, I jumped into the Hudson River just after dawn yesterday. Alongside 3,000 others, I swam, biked, and ran my way out of a trap of my own making.

It was my second Olympic triathlon, and the first time I had done the Nautica New York City Triathlon. Despite the heat, people came from more than 30 countries and all 50 states to compete.

Triathlons generally attract very, very fit people who love to exercise. I’m a little bit fit, and I sometimes like exercise. In my last triathlon, I finished near the back of the pack.

The city event was established in 2001, as part of New York’s bid for the 2008 Olympics, and now is one of the five largest triathlons in the country. Entries for the race went on sale in November and sold out in less than eight hours. The Accenture Physically Challenged National Championships are also part of the event.

The New York City Triathlon involves a one-mile swim in the Hudson River, a 26-mile bicycle on the northbound side of the Henry Hudson Parkway (which was closed to traffic between 4 a.m. and noon), and a six-mile run across 72nd Street and into Central Park.

As the bars closed in the city at 4 a.m. yesterday morning, the Upper West Side was overwhelmed by incredible athletes in Day-Glo spandex suits and huge duffel bags full of gear. Three sports means a whole lot of stuff, from goggles to bike shoes to energy gels that ooze into one’s mouth for fuel during the race.

To set up, athletes arrived before dawn to get organized and in “race mode.” While waiting for the race to start, the über-athletic compared aerodynamic bicycle wheels and hydration systems. I cursed the fact that I chose a sport that involves wearing spandex in public.

Getting 3,000 people into the water and racing is a feat of organizational wonder. The elite athletes, including the winner of the triathlon, Greg Bennett, who will race in Beijing next month, started the race off at 5:50 a.m. From then on, swimmers were arranged in heats based on age groups.

I wriggled into my wet suit around 6:10 a.m.; my start time was 6:23 a.m. My brother wanted to film me getting into the neoprene suit, but I told him he’d better not or the camera might end up in the water.

I was told that the current would make me “glide” through the water and that this swim would probably be my “PR,” or personal record. That’s the upside of swimming in the Hudson. The quality of the water is a downside, but I figured I shouldn’t put too much thought into it.

I was less than thrilled when my fingers combed through a jellyfish, however. I don’t think anyone else was too happy about them, nor were they forewarned about the possibility of masses of stinging jellyfish.

The beginning of the swim is a great mash of people, and it’s not unheard of to get an elbow in the eye. Eventually it thins out, unless one is slow, as I am, and overtaken by swimmers from other heats. I had my share of intimate encounters with my fellow triathletes, but had the good fortune to avoid facial injury.

Out of the water, it’s time for a costume change. Putting a wet suit on is like putting on rubber panty hose (some people use nonstick cooking spray to aid the process), but getting it off is a relative breeze. I had my trisuit on underneath: special, quick-drying bike shorts and a hot pink singlet, another quick-drying article that can go from sport to sport.

After 17 years of riding a fluorescent orange mountain bike, I had purchased a Cannondale on Craigslist and silver biking shoes that clip into the pedals. Biking up the Henry Hudson seemed a lot faster on the new bike, and I was feeling pretty good about it, until I realized that what I thought was the finish was, in fact, not the finish, and there were a few more miles to ride. But I rode them, and then was back at the transition area to change my sneakers and begin the run.

The run is both the best and worst part of the triathlon. The swim is over; I didn’t drown. The bike is over; I didn’t get a flat. Now it’s just me and my sneakers, headed over to Central Park.

The thing is, I was tired. I had already traveled many miles, and, having just gotten off my bicycle, my legs were like rubber.

But, this is what I signed up for. And Central Park is where I’ve done 90% of my training. Whenever I run or bike there, I feel like I’m in the heart of the city, the place people go when they need to be refreshed and readied for the rest of New York.

So when I joined the athletes running the loop — running the opposite direction that most people run, going down the Great Hill, not up it — I was tired and hot, but the finish line loomed. Several non-New Yorkers complained about the hills and found the run very difficult. I found it difficult, too, but at least I had a home-court advantage.

The park was full of people there to cheer on the athletes, but it was the athletes themselves who gave the most encouragement. I’m not used to people talking to me in the city, but during the run other athletes often said encouraging words as they passed me. This reminded me to keep smiling, long after the ink had worn off on the smiley faces on my hands.

The last quarter-mile seemed to last forever, prompting expletives from several runners who wanted it to come sooner. But after several hours of intense exercise on a 94-degree day, it was the most welcome thing in the world. Well, that and the open arms of the fans assembled there to cheer us on.