Today, 2,500 athletes will attempt to cross the finish line of the first-ever New York City Ironman Triathlon. (Not even the Hudson’s grimy waters could stop them.)

“This is a huge moment in the city for the entire triathlon community,” says Alison Kreideweis, triathlete, trainer, and co-founder of Empire Tri Club.

At the big event, Kreideweis will be acting as a volunteer, helping athletes with the transition from biking to running, but she’s been on the other end of that assistance many times before, so we asked her to give us some insight into what training to be an Ironman really entails.

Kreideweis is the co-founder of Empire Tri Club, which acts as a NYC community for triathletes.

1. Six months of your life. The typical training program, says Kreideweis, is 24 weeks long, which means you’ll be intensifying your workouts for half of a year. “If you have enough of a fitness base, you can do it in as little as 20 weeks,” she says. Still, it’s a long stretch.

2. Hours, lots of them. The number of hours spent training gradually increases until  a peak a few weeks before, and then tapers off as race day approaches (so you’re not totally spent when it’s time to go for it).

At the peak, you may be spending 1-2 hours training on weekdays and 7-8 hours per day on weekend days, with just one day off. Kreideweis shared her training log from an Ironman, and during her peak week, she completed 9.5 hours of biking, 6 hours and 17 minutes of running, and 2.5 hours of swimming to total 18 hours and 17 minutes of training.

3. Food as fuel. “Nutrition is the fourth sport,” Kreideweis says. “You can do all of the running, swimming, and biking, but there’s no way you can complete the race if you don’t have enough fuel.”  Triathletes have to carefully fuel while training, and even more so on race day, when many have stomach issues because of the stress on their bodies. They rely on portable nutrition like gels, powders, and power bars, have a special needs bag ready, and take salt pills to prevent cramping.