I would like to know more about the benefits of using a standing desk at work. Please provide [num_sentences] 4 sentences in your response. Highlight at least [num_highlights] 2 sections with markdown. Your answer should contain at least [num_placeholders] 2 placeholders such as [health issue] and [productivity level]. Also, include keywords [keywords] "ergonomic", "standing desk", "circulation", "energy".

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