Here's the problem: Your body is capable of absorbing one quart of water in an hour. In the same amount of time, it can use and lose two quarts of water. You are hiking in the heat and humidity for 17 hours, putting out more water than you are taking in.

Photo courtesy of Rachel Carson Trails Conservancy Hikers walk along Burtner Hill during the 2004 Rachel Carson Challenge. This year's event will be Saturday. Click photo for larger image. If you go: Rachel Carson Trail Challenge The ninth annual Rachel Carson Trail Challenge will be held on Saturday. Rather than a race, the "challenge" is not to "come in first" or "win," but to endure, to finish the 34-mile hike in one day. This year's Challenge starts at the Beaver Shelter at Babcock and Pearce Mill in North Park at sunrise, 5:50 a.m. and ends in Harrison Hills County Park. The deadline for finishing is sunset, 8:54 p.m. The entrance fee is $40 in advance and $50 the day of the Challenge and includes T-shirt, shuttle, checkpoint food, cookout and trail guide. For details and registration information: 412-512-4544 or www.rachelcarsontrails.org.

This problem began to bother me about 26 miles into the Rachel Carson Trail Challenge hike. In fact, it bothered me enough that just before the 31-mile mark, I was finished, 2.8 miles before the trail was.

Was I bummed? No way. I was excited by having hiked almost 31 miles in one day. I also remember the first time I attempted to do this hike. It was the year before.

But first, a bit of background.

Rachel Carson was born in Springdale in 1907. By profession, she was a marine biologist. For recreation, she hiked, watched birds, explored the outdoors and in general, was a nature enthusiast. In 1962, two years before she died, she published the book "Silent Spring."

Because of this book, the American public became aware of the dangers of pesticides and herbicides. "Silent Spring" criticized the negligence of industry and government agencies regarding issues concerning the environment. It was partially due to the support of President Kennedy that this book became a spearhead symbol and sort-of bible for the environmental movement.

A hiking trail extends 17 miles east from where Rachel Carson grew up in Springdale to Harrison Hills County Park in the extreme northeastern corner of Allegheny County. The trail also stretches 17 miles west to North Park. The trail is extremely varied, crossing several county parks, following power and gas lines, passing suburban homes and farms, fording creeks, meandering through woods and fields, and skirting the edge of steep bluffs. The trail terrain ranges from paved roads to some stretches that are quite primitive and rugged.

In 1975, this trail was named for and dedicated to Rachel Carson.

For the past eight summers, on the summer solstice, American Youth Hostels has staged a promotional hike in honor of Rachel Carson. The plan is simple: Celebrate the trail by hiking the whole 34 miles. In one day. Really. (This year's hike will be on Saturday.)

Photo courtesy of Rachel Carson Trails Conservancy Participants in last year's Rachel Carson Trail Challenge work their way down Burtner Hill. Click photo for larger image.

In general, I know very few people who enjoy going on long hikes. I know even fewer who would be nuts enough to be interested in a hike of this length. So I called my friend Will Viner, who said, "I'm there."

And with that enthusiasm and a little training, we reported to the registration table at 5:30 a.m. on June 22, the summer solstice. Twenty minutes later, we set out.

One of the reasons I look forward to hiking with Will is that he is capable of hiking at near-light speed, and I knew I needed a little lightning to help me keep a fast pace. After all, we had 34 miles to cover in only 16 hours of daylight.

Did I mention that Will brought his dog, Zoe?

Through the woods we went, passing suburban residential areas and farms, through a railroad yard, under endless power lines, along gas pipelines, across grasslands, up and down hills, through thick brush, past backyard swimming pools, horse pastures and convenience stores, crossing highways and swift streams, avoiding barking dogs and wiggling salamanders and beer-swigging truck drivers.

Our pace was a bit faster than I'm used to, and certainly faster than the pace I find comfortable. But I had been training for a several months, including taking a 14-miler, an 18-miler, and lots and lots of steep hills.

But there was Will, up ahead of me most of the time, glancing over his shoulder, smiling me on. And the dog had probably walked 34 miles during the first 17. You know how dogs walk -- back and forth, up and down, checking out this and sniffing out that. Well, crank it, good dog!

The temperature was up around 90 degrees, and the humidity was at some comparable number as well. I remember seeing one cloud that day. We took an extended water break at mile 17 to replenish our fluids.

The halfway rest stop was in the middle of a several-mile section of the trail called "The Roller Coaster." I couldn't remember ever seeing a real roller coaster as steep as these hills. By this point, the hike was becoming a matter of will. (I'm not sure how much intention is in this pun since, had Will not been there, I probably would have chosen to stop hiking long before.)

Certainly, conditioning counted for a lot, but I began to understand that it would be will power that would carry me through the entire Challenge. For the most part, what with the heat and moisture in the air, I felt OK, but I just couldn't seem to stop sweating. I didn't seem to be able to cool down.

We continued hiking, but around mile 19, I began to review the symptoms of heat prostration: difficulty in cooling down, continuous sweating, doing silly things, faulty memory. I couldn't remember all the things I learned about it. I briefly wondered about health risk.

At the same time, I was confident that if I could find and put down some Gatorade, I'd be strong enough to continue.

My mind wandered. I began to think about what I had learned about this trail, which one Challenge organizer had called "one of the toughest short trails in the whole United States." Another organizer, told me on the telephone before the hike, "What drives people to take this Challenge hike, I have no idea."

I wondered to myself what was driving me to do this hike. Bragging rights? Wearing the T-shirt? Holding back the effects of aging? The fun of hiking all day with a good friend? I decided: all of the above.

I found the inspiration to push myself up those very steep hills while pouring out perspiration. Will, on the other hand, had barely broken a sweat. "I don't know," he said. "It just works that way with me. I just don't sweat much."

"Don't you feel hot?" I asked.

"Sure. It's hot out here. It just doesn't bother me." Show-off.

I thought about the Mid State Trail hike I took with another friend. At the time, that hike was the most grueling, challenging hike I had ever done.

Well, Mid State Trail, step aside. You have been replaced. Never have I challenged myself like this before. In terms of sheer hike brutality, the Rachel Carson wins, hands down. Cool! But ...

We arrived at the water station at mile 20.5, which was 21 miles into the hike, as we had earlier taken a wrong turn at a poorly marked part of the trail. The organizers decided not only that the distance and the timing were a challenge, but also that there were sections of the hike that required trail-finding skill as well.

While there is no one I'd rather be lost in the woods with than Will -- in terms of his sense of direction -- trail finding can take time. It was due to Will's internal compass that we were able to find our way back from the section where we got lost earlier.

We pushed on, reaching mile 31 by about 8:30. This was a checkpoint, and here we met one of the race organizers. Gulping bottles of our replenishing electrolyte solution purchased at the nearby convenience store, we reviewed our situation.

Sure, after 31 miles we were tired. Sure, the next part of the hike looked like the steepest part yet.

Could we do this? Of course we could do this. What were we, wimps? But look at the time. Whirr and click went the gears in our heads as we calculated how far we still had to go.

Whoops, we would be finishing the hike in the dark. And we knew the last few miles of the trail to be through the woods, and we knew that the trail was poorly marked. If we got lost in the woods in the dark, we could end up there all night. Yuck.

On the other hand, we had come so far, and it was only three miles more. It might be worth the chance.

"Y'wanna try it?" I asked.

"Yeah, but you know, the prospect of spending a night in the woods unprepared is where lunacy turns into idiocy."

In the end, we chose to be disappointed lunatics rather than suffering, sickly idiots. So after putting in 31 miles in a long day, we called it quits. (Ooh, I hate that word.) One of the volunteers overheard our decision. She offered, "Hey, there's always next year." Alas, I would have preferred that she say, "Hey, 31 miles is incredible! You guys are the greatest!"

Ten minutes later, lying supine on the grass, still sweating, just catching my breath, I said, "I'm not making any decisions at this moment. Ask me later. We'll see by the next summer solstice whether I'm a lunatic or an idiot."

What a day! Not only were our bodies full of sore and depleted muscles, but at day's end, we exhibited an impressive exhibition of cuts and scrapes from the brush along the trail, as well as numerous bites and stings from flying things. The temperatures during the day were in the 80s, the humidity was in the 90s, and the precipitation was listed at 0.00 inches.

This hike was the toughest physical challenge I have ever accomplished.

Many people on the hike in their 20s and 30s complained that this day made them feel old. I was pleased that even though I was a decade or two older than that, the hike made me feel young.