Journalist and Born to Run author Christopher McDougall has said that barefoot runners care more about how smooth a running surface is than how hard it is. That’s because when skilled minimalist running technique is paired with the maximal sensory feedback provided by the unshod foot, a runner on a hard but smooth concrete sidewalk compensates through slightly greater knee flex to dissipates the landing shock effectively. And compared to a more rugged surface, the runner is less likely to encounter injury of the sudden traumatic kind that could result in bruises, lacerations, or even fractures. But could there be long-term benefits to running on irregular surfaces with adequate but not too much protection on the bottom of the foot?

“Any surface that’s completely even will lend itself to very stereotypical loading, and we know that repetitive stress injuries occur from doing things over and over again with unvarying motion.”

—  Daniel Lieberman

Repetitive stress injuries from running can occur when the body performs the same action with little or no variation, over an extended period of time. Given this, it may be advantageous to not always run on smooth, uniform surfaces. Running barefoot or in a thin-soled minimalist shoe or sandal over rough but tolerable ground forces the runner to continuously shift direction, adjust speed, and vary the way the feet land. This diversifies the stresses all the way up the legs, potentially reducing the chance for overuse injuries, strengthening the feet and ankles in a variety of positions, and challenging balance and coordination. Additionally, incorporating hills, trails, dirt farm paths, grassy surfaces, and lots of twists and turns into your running routes can reduce boredom and yield psychological benefits through focused attention or mindfulness.