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One athlete's "psych-up" ritual may psych out an opponent. And even treatments that lack hard evidence of benefit, scientists say, might provide a competitive edge if the athletes believe they work.
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At 31, Michael Phelps became the oldest swimmer to win an individual event. Katie Ledecky won her second race in Rio. And Simone Biles led the U.S. gymnastics team to a win of historic proportions.
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You can't follow everything in Rio, but you want to catch the highlights. Here's a guide to the American athletes and events likely to produce the most memorable performances.