(NEW YORK) So many trails, so little time. With summer around the corner in the Pacific North-west, Dan Lauren, 48, faces this frustrating state of affairs every weekend.

Most weekends, Mr Lauren, a technology manager at Weyerhauser, a timber company in Federal Way, Washington, gears up for at least one heart-thumping trek of 16.1 km to 32.2 km. In March, he and four friends from a mountaineering club powered through 50 km and more than 4.3 m of elevation between 5.30 am and 9 pm.

The goal, Mr Lauren said, was simple: to knock off as much elevation and as many miles as quickly as possible.

'This was not a scenic 'go see the beauty of the wilderness' outing,' he said. 'Instead, it was 'How fast can we get up and get down? How can we maximise our conditioning?''

Outdoor adventurers call this pastime speed hiking. It combines the muscle-building benefits of altitude gain with fast-paced aerobic activity, which keeps heart rates high. Fast hikers usually wear lightweight footwear and hydration backpacks and minimise what they carry. Most trips are done in a day. No organisation tracks the number of speed hikers, but a growing number of outdoor enthusiasts are hiking for fitness, and many have turned to speed hiking for results, said Clint Wall, the research manager at the Outdoor Industry Association, a trade group in Boulder, Colorado.

Speed hiking isn't for everyone. Plenty of hikers still prefer hitting the trail leisurely with heavy boots, a hefty backpack and enough trail mix and gear to spend nights under the stars.

Jane Huber, the author of 60 Hikes Within 60 Miles: San Francisco is a traditionalist. In an e-mail exchange she argued that a leisurely pace allows more discovery. 'I like to stop and smell the manzanita bushes,' wrote Ms Huber, who also edits Bay Area Hiker, a website. 'The slower I hike, the more I see, hear, smell, even taste (during blackberry season).'

But on any given day there's little time for dawdling, time-pressed hikers say. Some fast hikers don't bother tackling epic journeys. They stick with quick jaunts to boost fitness.

After nearly a decade of gym-going, Morgan Phillips, 43, gave up last year, choosing an intense workout on the steep and deserted Vasquez Trail in Garland Ranch Regional Park in California. The trail climbs nearly 610 m in 1.6 km , and Mr Phillips, a sommelier at Sierra Mar, a restaurant in Big Sur, hikes up and back in roughly 40 minutes. He pants. He groans. And by the time he returns to his truck at the trail head, he's dripping with sweat, energised for a night of work.

'Regular hiking would be too slow, and running would be too fast, but this pace is perfect,' Mr Phillips said, noting that Gus, his 4-year-old Boxer mix, usually accompanies him.

Some speed hikers mix in running. Every Wednesday, Art Messal, 28, leads a dozen members of a Boulder trail-running group into the foothills of the Rocky Mountains. They hike out quickly and jog back.

'The whole idea is to provide people with the opportunity to get out there and combine being out in nature with working out,' said Mr Messal, a software engineer in Estes Park, Colorado. 'Most of us can't run 30 miles up a mountain, but we can move quickly.'

Moving quickly on uneven terrain has its pitfalls, though. It's relatively easy to fall and to bruise your hands or injure your forearms. Out on the trails many hikers call this injury 'foosh', for 'fell on outstretched hand.'

Ryan Jordan, the publisher of Backpacking Light magazine in Bozeman, Montana, said that he and backpackers he knows have suffered their share of twisted ankles, pulled hamstrings and strained quadriceps.

Jeff Kunkle, a speedster who hiked the Grand Canyon, offered this advice: 'The whole idea of speed hiking is relentless forward motion, but at the end of the day if you're not feeling right, there's no harm in slowing down.' - NYT