You can (and should) still exercise.
Hall, 30, has been dealing with setbacks since the beginning of his college career at Stanford, where he got off to an injury-riddled start after becoming California's high school cross country champion in both his junior and senior years. The mental grind of contending with injury, he points out, "is not all in your head." He typically runs twice a day, which means he gets two endorphin rushes daily. "[If an injury requires complete rest], then I'm missing a huge daily dose of endorphins that promote positive thinking and well-being," he says. "I think this is a major factor why a lot of runners go into a mild form of depression when injured. That's when cross-training becomes very important, because you can at least get an endorphin release and maintain some sort of fitness." So, try any other sport that doesn't aggravate your injury – you're mainly going for endorphins here – and the positive feeling that ensues will keep you motivated and pumped for future runs.