James Fallows is a national correspondent for The Atlantic and has written for the magazine since the late 1970s. He has reported extensively from outside the United States and once worked as President Carter's chief speechwriter. His latest book is China Airborne.
"The collision of the heel with the ground generates a significant impact transient, a nearly instantaneous, large force. This force sends a shock wave up through the body via the skeletal system." Scientists on what can happen when you run.