bicycles

Cheap knock-offs don't provide anywhere near the protection or durability of the products they replace. And most riders won't be able to tell the difference between real and counterfeit helmets.

Autonomous vehicles have gotten pretty good at detecting other cars and pedestrians. But "seeing" bikes and predicting what they'll do is still a challenge. The answer may lie in bikes themselves.

Women in prison often eat to relieve stress or boredom. The resulting weight gain can make other physical and emotional problems worse. In one prison, spinning helps keep the pounds and rage at bay.

In New York City, an instructor leads an indoor cycling class while participants at home around the country ride along — and compete with other riders — on special bikes outfitted with tablets.