The laces on the left are tied in a strong knot that lies horizontally. The laces on the right are tied in a knot that makes the bow lie vertically and which, according to new research, can come untied more easily.
Dr. Tonatiuh Barrientos Gutierrez, an epidemiologist in Mexico City, jogs near his home in the southern part of the capital. He says it's hard to run on the city's streets.
Meghan Dhaliwal/for NPR
The researchers were inspired by working with ultramarathoners, who can be sidelined by blisters despite years of training. These runners competed in the 2007 Badwater Ultramarathon in Death Valley, Calif.
Izaic Yorks, a senior at the University of Washington, recently ran a mile in 3:53 — the fastest mile of any American collegiate athlete. Here, he competes on Feb. 27 in Seattle.
Stephen Brashear/Red Box Pictures
Haneen Radi, an Arab Israeli, wants to organize a marathon for her town of Tira, but was told the run couldn't include women. When she insisted, she received threats, and the back window of her car was shot out.