by Jason Koop, CTS Coaching Director and author of “Training Essentials for Ultrarunning”
Chances are, if you are asking the question, you should power-hike (walk). At slower speeds, walking is a more economical form of locomotion than running. It is only when you speed up to near the 12-min/mile range on level ground that walking is less economical (Falls and Humphrey 1976; Margaria 1976; Glass and Dwyer 2007).
The practical decision to run or power-hike has to do with both the situation you are in and the difference in energy costs between the two forms of locomotion.
While most elite runners, particularly at the 50K and 50-mile distance, will choose to run anything they can in order to finish faster, they knowingly do so at the expense of economy and have to spike their efforts up the steepest climbs in order to continue running instead of slowing down to a power-hike.