Why This Debate Exists
Ten years ago, this wasn't a debate. You went hiking, you wore boots. That was it. Then a wave of PCT and AT thru-hikers started finishing 2,600-mile trails in Altra Lone Peaks and Hoka Speedgoats, and the hiking world collectively asked: "Wait, you can do that in running shoes?"
Now the pendulum has swung hard toward trail runners, especially in the ultralight and thru-hiking community. But I've spent enough time in both — and made enough mistakes in both — to know that neither is universally better. I blew out an ankle in trail runners on a talus field below Glacier Peak. I also got blisters that ruined a trip while wearing stiff leather boots on a hot August day on the Pacific Crest Trail. The right footwear depends on three factors: your pack weight, your terrain, and your ankles.
Factor 1: Pack Weight
This is the variable most people overlook, and it's the most important one. There's an old rule of thumb that for every pound on your feet, you expend the same energy as carrying five pounds on your back. Whether the exact ratio holds up to scientific scrutiny is debatable, but the core insight is correct: heavy footwear costs you significantly more energy per mile than heavy pack weight.
Here's where it gets interesting. A pair of Altra Lone Peak 7 trail runners weighs about 1 lb 5 oz (595g). A pair of Salomon X Ultra 4 GTX hiking shoes weighs 1 lb 14 oz (850g). A pair of Scarpa Zodiac Plus GTX boots weighs 2 lbs 10 oz (1,190g). Over a 20-mile day, the energy difference between the Altras and the Scarpas is real and measurable in how your legs feel at mile 18.
But — and this is the critical but — trail runners were designed to support the weight of a runner's body, not a runner's body plus a 35-pound pack. If your base weight is under 15 pounds and your total pack weight is under 25 pounds, trail runners handle the load fine. As your pack weight climbs above 30 pounds, the lack of midsole stiffness in trail runners starts to matter. Your feet flex more with each step, which means more fatigue in the small muscles of your foot and more impact transmitted to your knees. At 35+ pounds, I want a stiffer midsole — which means at minimum a hiking shoe like the Salomon X Ultra 4, if not a light boot.
Factor 2: Terrain
Well-maintained trails with moderate elevation change? Trail runners all day. The PCT through Oregon, the JMT outside of the passes, most AT sections — these are superhighways by backcountry standards, and lightweight footwear lets you move faster and more comfortably on groomed trail surfaces.
Off-trail scrambles, sustained talus, rocky ridgelines, and technical terrain? I want a boot. I learned this lesson descending from Spider Gap in the Glacier Peak Wilderness, picking my way down a boulder field in Hoka Speedgoat 5 trail runners. Every step on those wobbly, angular rocks sent my ankles into extreme angles that the shoes couldn't stabilize. I was walking at a crawl, placing each foot with surgical precision because one wrong step on a shifting boulder meant a rolled ankle — or worse. A stiff boot with ankle support would have let me move through that terrain twice as fast with half the mental effort.
Stream crossings are another consideration. Trail runners dry in 30-60 minutes after a stream crossing. Boots take half a day or more, and waterproof boots filled with water are the worst of all worlds — heavy, sloshy, and they breed blisters like nothing else. If your route involves multiple stream fords (looking at you, early-season Sierra crossings), trail runners win decisively.
Factor 3: Your Ankles
This is personal and nobody can answer it for you. Some people have strong, stable ankles from years of sports or just good genetics. They can hike 20 miles in minimal shoes on rocky terrain without issues. Other people — myself included — have ankles that roll if you look at them funny. I've sprained my right ankle three times on trail, all in low-cut shoes, all on terrain I thought was "easy enough" for trail runners.
After the third sprain, I started doing ankle strengthening exercises (single-leg balance on unstable surfaces, resistance band work, calf raises). These helped more than any boot could. But I also started being more honest with myself about when I need the external support of a boot. On a groomed trail with a light pack, my ankles are fine in trail runners. On a long off-trail day with a loaded pack, they're not, and no amount of ego will change the biomechanics.
If you have a history of ankle injuries, consider a mid-cut hiking shoe as a compromise. The Salomon X Ultra 4 Mid GTX provides more ankle support than a trail runner without the weight and stiffness of a full boot. It's the shoe I reach for most often when I'm unsure about the terrain.
The Hybrid Approach
Here's what I actually do: I own both, and I choose based on the specific trip.
Trail runners (Altra Lone Peak 7) for: day hikes on established trails, thru-hiking on maintained tread, hot-weather hiking, any trip where stream crossings are expected, and fastpacking.
Light hikers (Salomon X Ultra 4 GTX) for: 3-season backpacking with moderate pack weight, shoulder-season hiking where I want some water resistance, mixed terrain with some off-trail sections.
Boots (Scarpa Zodiac Plus GTX) for: heavy pack weight (30+ lbs), technical terrain with significant scrambling or talus, winter hiking, and any trip where I'll be on snow or need crampon compatibility.
This three-shoe approach means I'm never forcing the wrong tool into the wrong situation. It also means I own three pairs of hiking footwear, which my wife finds excessive and I find entirely reasonable.
Breaking In: Boots vs Trail Runners
Trail runners need essentially zero break-in. Take them out of the box, go hike. If they hurt in the store, return them — no amount of "wearing them around the house" will fix a bad fit in a trail runner.
Modern hiking shoes are similar — the Salomon X Ultra 4 was comfortable from the first mile. Full leather boots, however, still require a break-in period. My Scarpa Zodiac Plus GTX needed about 40 miles before the leather softened enough to stop creating hot spots on the outside of my foot. I did those 40 miles on local trails before taking them into the backcountry. Breaking in boots on a multi-day trip is a recipe for blisters and misery.
Durability: The Hidden Cost
Trail runners wear out fast. My Altra Lone Peaks last about 400-500 miles before the midsole compresses enough that I start feeling rocks through the sole and the tread lugs wear smooth. At $140 a pair, that's roughly $0.30 per mile. My Salomon X Ultra 4s have about 800 miles on them and still feel supportive, putting them around $0.22 per mile so far. My Scarpa boots? I've had them for three seasons — probably 600 miles — and they look like they'll last three more, which would bring the per-mile cost well below $0.15.
For a weekend hiker doing 100 miles a year, the cost difference is trivial. For a thru-hiker burning through 3-4 pairs of trail runners on a single long trail, the math adds up. Some PCT hikers spend $500-600 on footwear for one thru-hike. But most of them still prefer trail runners because the comfort and performance benefits outweigh the replacement cost.
My Honest Take
If you're starting out and buying your first pair of hiking footwear, get the Salomon X Ultra 4 GTX. It splits the difference perfectly — lighter than a boot, more supportive than a trail runner, waterproof enough for three-season use. Once you've done enough hikes to understand your own feet, ankles, and terrain preferences, you'll know whether to go lighter (trail runners) or burlier (boots) for specific trips.
If you're already experienced and asking this question because you're curious about switching from boots to trail runners: try them on a day hike first. Then a short overnighter. Give your ankles and foot muscles time to adapt to less support. Most people who make the switch love it. But make the switch gradually, not on day one of a 200-mile trip.
