Shovelling snow can put strain on your heart. How to stay safe as millions dig out

In July of 1979, Ronald Reagan, then eighteen months from the presidency, was taken to see the North American Aerospace Defense Command, better known as NORAD. The underground facility, jointly run by the United States and Canada, is carved inside Cheyenne Mountain, near Colorado Springs. In one widely cited account of the visit, many on the tour were visibly awed by the scale and seriousness of the operation. But when Reagan asked what the US could do to stop a nuclear missile, the answer shocked him: nothing. As the story goes, Reagan was told that all NORAD could do was track incoming...