Barefoot running on pavement

Pavement is where minimal running is hardest, and it is worth being specific about why rather than just saying "concrete is hard."

1. No compliance. Dirt and grass deform under your foot and absorb a share of each landing. Concrete does not deform at all, so your foot and the sole absorb everything.
2. Relentless repetition. On trail, every stride is slightly different — different angle, different pressure distribution, brief micro-rests for different tissues. On a road, every stride loads the same structures the same way, thousands of times.
3. Camber. Roads are domed to drain. Run along one for an hour and one foot has been pronating more than the other for an hour.

Point two is the one people underestimate. Variety is protective, and pavement removes it.

For regular road mileage, most people's practical floor is 8 to 10 mm. The Xero HFS II at 8.5 mm front and back is about as thin as road running gets without an extended build-up; the Speed Force II at 7 mm is a shorter-distance proposition.

This is the point in this category where stack height stops being an ideological question and becomes a load-management one. Systematic reviews report moderate evidence that minimalist shoes increase forefoot pressure relative to conventional running shoes, and thereby metatarsal stress-fracture risk. Concrete is where that pressure is highest.

A mistake worth avoiding: treating treadmill, trail and road mileage as interchangeable. They are not. A belt is softer, consistent, and partly pulls your leg back for you. Trail is softer and more varied. Road is harder and more repetitive than both.

So when you add road, add it at roughly half your established distance elsewhere, and grow it on its own progression. Treadmill picks and the full running transition.

• Raise your cadence slightly. A quicker, shorter stride reduces peak force per step. This is the one form cue worth working on deliberately — unlike forcing a forefoot strike, which loads your calf and metatarsals harder at the same time.
• Run on the flattest part of the road or on the pavement center. Avoid spending whole runs on the camber, and swap sides periodically if you must use it.
• Mix surfaces within the week. Some road, some trail, some treadmill. The variety is protective in itself.
• Keep a cushioned pair for your longest runs. The split is a permanent, perfectly respectable setup rather than an unfinished transition.

People do it, and plantar skin genuinely toughens over months. It also exposes you to glass, metal, thermal burns from hot asphalt and infection risk from cuts you did not notice — and it removes the one thing a thin sole was still providing. We are not going to recommend it, and we are not going to lecture anyone who does it carefully on surfaces they know.

What we would say: if you want the strengthening stimulus, a 4 mm shoe gets you most of the way there with none of the laceration risk.