Hal Koerner's Field Guide to Ultrarunning: Training for an Ultramarathon, from 50K to 100 Miles and Beyond

we run a marathon, we are undertaking around 35,000 strides. That’s 35,000 x two-and-a-half times our bodyweight coming back at us. We can either use these 35,000 opportunities to load our body well and create elastic energy to propel us forwards or we can suffer all of that impact, which will in turn slow us down and potentially hurt us.

Training for Endurance, by Phil Maffetone. Stamford, New York: David Barmore Productions, 1996. In Fitness and In Health, Phil Maffetone. Stamford, New York: David Barmore Productions, 1997. Cheng Hsin: the Principles of Effortless Power, by Peter Ralston. Berkeley: Blue Snake Books, 1989. Why We Get Fat: And What to Do About It, by Gary Taubes. Ne

Shock absorption is particularly important in marathon running, since the feet of long-distance runners contact the ground an average of 10,000 times per hour, absorbing between two and seven times their body weight with each strike.

As Christopher McDougall describes our ancestors in his book Born to Run, running was hardwired in such a way that it was indispensable to survival:

Never go two days without running. —Hal Higdon, runner and writer