1. Work More Than Just Your Legs

This is really about translating glycogen-depleting exercises to the great outdoors for a full-body workout. King recommends doing pullups from low tree branches and lugging heavy rocks uphill. “When I was training for obstacle races, I’d pick up a rock midrun, throw it on my shoulder, and hike up a steep hill.”

2. Do the Real “Mountain Climber”

When he’s prepping for a mountain race, King spends more time hitting steep technical trails that require hiking and some Class 2 scrambling, using both feet and hands. It’s a killer full-body workout that engages the upper body and core—needed for balance over rocks—in ways that flat running simply can’t match.

3. If You’re Walking, Walk Uncomfortably

 Even pro runners hike when things get too vertical. King advises going off-trail and exploring supersteep, gnarly terrain that’s impossible to run. “You may not be working on your aerobic capacity as much at that point,” King says, “but you’ll be working other things—balance, core strength, and legs.”