Provide a detailed explanation of the benefits of regular physical activity, focusing on how it improves mental health. Your response should contain at least 5 sentences. Highlight at least 2 sections in your answer with markdown, i.e. *highlighted section*. Include keywords *endorphins, serotonin, anxiety, depression, mood*. At the end of your response, please explicitly add a postscript starting with *P.S.*.
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