The entry list for this year's Grand Slam of Ultra-running in no way resembles that of an elite road marathon field. No, this merry band of 22 rookies and warriors--or foolhardy ones, depending on your perspective--isn't typical.

For those who finish, most will never do it again. But anomalies exist. The youngest is 29-year-old Brad Bishop of Denver, racing his second Slam, training mostly by running to and from work, with an eye toward breaking the record of most completed lifetime Slams (Dan Brenden with eight).

The oldest is Thomas Green, 63, of Maryland, also competing in his second Slam--and likely his final one. Back in 1986, at age 35, Green was the only finisher for the inaugural summer-long event.

In the 28 years since then, the Grand Slam has been completed 288 times: 248 by men, 40 by women, totaling 254 different people (215 men, 39 women).

These athletes will attempt to complete four of the oldest 100-mile races in a span of 10 weeks, beginning with the Western States 100 on June 28-29. Western is followed by the Vermont 100 three weeks later, on July 19-20; the Leadville Trail 100 Run on Aug. 16-17; and finally, the Wasatch Front 100 on Sept. 5-6.

No course is easy. Western States, starting in Squaw Valley, California, cooked in 2013 under 110-degree temperatures. Vermont's course, hot and humid, slowly wastes away runners' legs with its undulating hills, ascending and descending 14,000 to 15,000 feet. At Leadville, no part of the course is lower than 9,200 feet (and the route goes as high as 12,600). Wasatch, through Utah's northern mountains, features varied terrain and some 26,000 vertical feet of climbing. No type of weather is off-limits--there have been below-zero days and some that have soared above 100 degrees.

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And the Slam is not cheap. Without factoring travel, food, accommodations and mob, entry fees alone will cost a single runner more than $1,000 for the summer. Being able to attempt a Slam at all requires acceptance through a lottery at the Western States, where an athlete's name is drawn an average of once in five years. For those who haven't qualified for Western through performance standards, getting a coveted spot means it's now or never if they're considering the Slam.

Rest, Recover, Race

Few participants are after any records or battling other runners. The time spent between races is less about actually training than consciously and dutifully recovering before it's time to punish the body again. The sole focus is rest, recovery and sleep--meaning little or no running, except for a handful of days leading up to the next race.

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Rest, Recover, Race.

Ultimately, this approach robs many athletes of aerobic capacity and speed through the summer. The final race, Wasatch, already considered the hardest of the bunch (most runners finished in more than 30 hours last year), becomes even harder for those who dare the Slam.

Abby McQueeney Penamonte, of Denver, took 27 hours at Wasatch, ending up with the fourth-fastest Slam time ever among females, just slightly more than 96 hours. To do that, she ran 90-100 miles per week, including climbs totaling some 20,000 vertical feet.

"You spend a lot of time during the summer not logging a bunch of miles because you're racing," she says. "I probably should have taken a bit more rest."

The suffering, not surprisingly, forms bonds. Many runners kept in touch, congratulated and motivated one another, and asked questions through a Facebook page.

But why do these runners go after a goal that so few in the world have heard of or understand in the first place?

"It was something that always intrigued me," Penamonte says. "I wanted to test my body and see--and I thought it was a once-in-a-lifetime."

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