After competing in a few marathons and short triathlons, recreational athletes who crave something bigger often start dreaming about the next great challenge: An Ironman.

The grueling three-stage race pushes competitors to swim 2.4 miles and bike 112 miles before running a full marathon. The average finishing time for an Ironman race, according to, is 12 and a half hours, though some athletes stay on the course for as many as 17 hours.

Such an extreme physical endeavor may seem impossible. But with enough time, planning and dedication, experts say, most people can make it happen.

PHOTOS: 10 Techs Transforming Sports

“Anybody, if they have the desire, can definitely finish,” said Mark Allen, a six-time Hawaii Ironman world champion, head coach at, and author of “Fit Soul, Fit Body: 9 Keys to a Healthier, Happier You.” “The biggest thing is taking time to slowly build up fitness and let the body adapt to training.”

That doesn’t mean it’s going to be pain-free.

“No matter who you are, even if you are a top professional, even me, when I started training every January, the first 30 or 40 minute run was tough, and I thought, ‘Gee, if that’s tough, how am I going to finish a marathon after the bike and swim,” Allen said.

“The distances seem out of the realm of possibility. But in Hawaii, people over 80 have finished, and people who are far from lean and mean have finished. You don’t have to be like a greyhound to finish an Ironman.”

For would-be competitors with no triathlon experience, Allen said, it can take up to three years to build enough fitness and triathlon experience to get to the starting line of an Ironman. Even athletes with a solid base in each sport should allow about a year to prepare.

As training progresses, the goal should be to do two weekly workouts in each sport, Allen said. One of those sessions should be for speed. The other should be for endurance with distances that grow by about 10 to 15 percent each week to a limit of about 4,000 yards in the pool, 100 miles or five and a half hours on the bike and two and a half hours of running. Tapering, or a gradual decline in distance, should begin about a month before race day.

Every other week, Allen added, it helps to practice the transition from biking to running because leg muscles that shorten up on the bike need to stretch out to run efficiently. Training for the changeover teaches the body to loosen up more quickly.

With a month to go, competitors should know what they’re going to wear throughout the race and how they’re going to handle the transitions between sports. Shorter races leading up to the main event are good opportunities to figure out the details and get out the kinks.

Scott Barbour/Getty Images

What you eat matters, too, said Jamie Cooper, a nutritionist at Texas Tech University in Lubbock, and author of The Complete Nutrition Guide for Triathletes: The Essential Step-by-Step Guide to Proper Nutrition for Sprint, Olympic, Half Ironman, and Ironman Distances.

When exercising for a half day or more, Cooper said, athletes need to pay attention to three categories of intake: fluids, carbohydrates and electrolytes.

VIDEO: Marathon Running Examined

You can figure out how much liquid you’d need during an Ironman by calculating your personal sweat rate. Weigh yourself before and after an hour-long run. Each pound lost equals 2 or 3 cups of fluid needed per hour. Depending on how drippy they get, Cooper said, athletes need between 2 and 6 cups each hour.

For any event that lasts longer than two hours, she added, competitors should plan on consuming 60 to 70 grams of carbohydrates per hour in the form of simple sugars because carbs are the body’s main source of energy. Most sports nutrition gels, bars and other products are designed to supply the right kinds of carbs, she said. Other good options include jelly or honey sandwiches or candy.

After several hours of exertion, Ironmen and Ironwomen need to replace the sodium that comes out in their sweat, too, and Gatorade does not have enough electrolytes to replenish the salt lost during such a long race. Instead, Cooper said, competitors should take electrolyte tablets at the rate of about 500 to 1,000 mg per hour.

“Training is important,” Cooper said. “But in order to execute all the fitness and training you’ve done, you have to have the right nutrition. You have to be fueling properly.”

No matter how well you’ve prepared, Allen added, getting into the right state of mind is essential.

“If you’re doing an Ironman, you have a lot of time out there by yourself,” he said, often dealing with heat, energy lows and physical discomfort. “There’s plenty of time to come up with a few negative thoughts. ‘What am I doing here? Why did I think I should do this crazy race?’”

“I always tell people, when you see these moments happen in your training, those are perfect times to practice how to deal with it in the race,” he said. “When you start whining to yourself, take a breath and feel peace out there. There’s fulfillment in moving your body like that. Nobody said it was going to be easy.”