From triathlons to marathons, endurance sports have become a popular challenge for celebrities like Jennifer Lopez and Oprah Winfrey. Of course it helps to have a top-notch coach to guide you. Wes Okerson has trained and run with some of Hollywood's brightest stars, including Katie Holmes, who he prepared for last year's New York City Marathon. He tells us how he gets his famous clients ready for race day and what you can do to accomplish your training goals.

Q. How do you prepare clients for marathons?

A. "I've dealt with people who have little or no experience in long distance running, which is the first challenge. When you prepare for a marathon, it's mainly about building up mileage to a point where your body-and mind-can handle 26 miles. After a couple months of increasing your mileage, I recommend doing two short runs (4 to 5 miles), two intermediate runs (6 to 8 miles) and one long run (10 to eventually 18 miles) per week. Completing 40 to 50 miles a week puts you on track."

Q. What suggestions do you have for fitting training into a busy schedule?

A. "Mapping out a schedule each week is crucial. Pick a day of the week when you know you're not busy and make that when you'll do your long run. Sunday is usually good because people are off from work. Make an effort to fit in short or intermediate runs before or after work, but be sure to space them out so you're not running late in the evening and then early the next morning. You want to give your body about 24 hours to recover between sessions."

Q. What do you say to those who don't think they can finish a marathon?

A. "It is doable. For first-timers, running 26 miles sounds like an eternity, but your body gets to the point where running becomes second nature. If you're healthy and willing to train for it, you can do it."

Q. What common training mistakes do people make?

A. "They don't run far enough. If you've only done 12 or 14 miles, you're going to have trouble completing 26. On the other end of the spectrum, there are people who are doing way too much. They're abusing their bodies and getting overuse injuries. You don't have to do an excessive amount of mileage. As long as you have a plan in place and are running four to six days a week and resting at least once a week, you should be fine."

Q. What sort of cross-training do you recommend?

A. "Cross-training is vital because it enables you to give your running muscles a rest and use your body in a different way. With running, you're only moving in one plane with one motion and it can be very stressful on the joints. It doesn't matter what activity you do to cross-train as long as you're keeping your heart rate at 60 to 70 percent of your maximum. I tell people if they swim or play sports to continue to do so, but not in place of running. At the end of the day, it's about building up miles, so you shouldn't cross-train more than a couple times a week."

Q. How do you avoid "hitting the wall?"

A. "The wall is that point where you feel like you physically can't go on. It's usually a nutrition issue. Your muscles store enough fuel for about two hours worth of physical activity and when that's used up, you need another source of energy. You should be consuming food every eight miles and drinking water or half a cup of Gatorade every few miles. Energy gels are great because your body absorbs them much faster than solid foods. If you carb up the night before and are drinking and eating during the race, you should have enough fuel left in the tank to finish."

Q. What tips do you have for staying on pace during the race?

A. "When the race begins, you're really amped up. There are so many runners around you, everyone's moving at different speeds and there are always people passing you. Don't make the mistake of going out too fast. I recommend getting a heart rate monitor, which you can find at any sports store, to get an idea of how hard you're working at various speeds during your runs. You should train at a pace that keeps your heart rate at 60 to 70 percent of your maximum. If it's above or below this zone during the marathon, you'll know you're off pace."

Q.Do you have any advice for dealing with aches and pains?

A. "The marathon is a fun race, but it will definitely beat up your body. It is an extremely repetitive movement for the knees and ankles. If you start to feel sore during your training, ice your joints once a day for 20 minutes after your workout to keep the inflammation down. Make sure you take care of yourself."