As most Pittsburghers long for warmer weather, two residents head off next month to the frozen north and the frozen south to compete in endurance races.

On March 10, Katherine Belendiuk, 25, a graduate student at the University of Pittsburgh, plans to run in the Antarctic Marathon. The 26.2-mile race course on King George Island off the tip of the Antarctic peninsula loops through the scientific research bases of Uruguay, Chile, China and Russia.

March is near the end of summer in Antarctica. Temperatures for the race typically range from -30 to 15 degrees Fahrenheit, though the wind chill makes it seem about 10 degrees colder.

Conditions in Antarctica then may seem balmy compared to those Bob Struble, 58, a partner in the law firm of Meyer, Unkovic and Scott, is likely to encounter in the Iditarod Trail Invitational in Alaska beginning March 1.

The Iditarod is a dogsled race over the 1,150 miles from Anchorage to Nome, conducted annually since 1973 to honor the dogs and men who, in 1925, braved the Arctic winter to deliver lifesaving vaccines to Nome, which was suffering from a diphtheria epidemic. In 1989, four cyclists joined the race. In 1992, a runners' division was added.

Mr. Struble is one of 47 athletes worldwide -- 13 of them Americans -- selected to run or bike in the Iditarod Trail Invitational. He is one of 11 who plan to run a 350-mile portion of the trail, from Knik Lake near Iditarod to McGrath. Another 26 plan to cycle the distance, and two plan to traverse it on cross-country skis. Three plan to cycle and five plan to run the entire 1,150 miles.

Ms. Belendiuk has only been running for two years.

"In 2007, I made a New Year's resolution I wanted to run a marathon," she said. She ran in the Marine Corps Marathon in Washington, D.C., that year, and again last year.

In 2007, she became acquainted with Gunnery Sgt. Jimmy Shields, whose example has inspired her to run the Antarctic marathon. Last year Sgt. Shields ran the 110 miles from Tun Tavern in Philadelphia, where the Marine Corps was formed in 1776, to the starting line of the Marine Corps Marathon, to raise funds for the Semper Fi Fund, which provides aid to injured Marines and their families.

"Part of the reason why I'm doing this is to raise awareness of the [Semper Fi] fund," Ms. Belendiuk said. "I want to do something to help those who have given so much for our country."

Ms. Belendiuk's stepfather, Patrick McGann, is a Marine veteran of Vietnam, and her stepbrother, Patrick McGann III, is a Marine reservist. Ms. Belendiuk's boyfriend, Chris Connor, was a soldier in the 3rd Infantry Division who served three tours in Iraq.

Ms. Belendiuk runs 40 miles a week, and swims two or three times a week.

"Marathons keep me in balance," she said. "I find that if I don't have a marathon to hold me accountable, then it is more difficult to train."

Ms. Belendiuk, who is from Potomac, Md., has little preparation for the cold she is likely to experience in Antarctica. But, she said, "Pittsburgh, with all the hills, actually mimics the training conditions pretty well."

Mr. Struble wrestled and ran cross-country in high school, but then led a relatively sedentary life.

"When I hit 39, I tried running around the block, and it was kind of hard," he recalled.

After that wakeup call, Mr. Struble got into running big time. He favors ultramarathons, like Ohio's Buckeye Trail 50K (30 miles) in which he competed in January.

"I do marathons just for training," he said. He typically trains only three or four days a week, but usually has six-hour runs on both Saturday and Sunday.

The Iditarod Trail Invitational will be the longest race in which he's competed. He expects it will take him about 10 days to finish.

Before my body starts wearing out any more, I want to push it to the limit," Mr. Struble said.

Runners in the Iditarod Trail Invitational will be pulling a sled behind them, carrying their sleeping bag, food, a stove, and cold weather gear. Mr. Struble has added spinning and weightlifting to his workout regimen to help him prepare for the additional challenge.

Mr. Struble has only worked out once in conditions approximating those in Alaska. On the weekend of Jan. 16, he took his sled and gear to Linn Run State Park near Ligonier and spent the night. He learned a valuable lesson.

"It was minus 10 around midnight," Mr. Struble recalled. "I made the mistake of not getting into my sleeping bag right away. As soon as you stop exercising you've got to get back into a down sleeping bag to keep the heat you've worked up."

But Mr. Struble made himself something to eat before he crawled into his sleeping bag. By the time he did, his feet were cold.

"A sleeping bag is like a thermos," he said. "If you put in something cold, it stays cold."

Mr. Struble said he's prepared for the physical exertion required to complete the race. His concern is for adapting to the cold, and if he should twist an ankle or otherwise injure himself on the race course.

"The body can keep on going," he said. "It's the mind that wants to stop."