What’s an acceptable baseline of fitness? What should you be able to do off-the-couch? For some people it’s running a mile. For others, it’s a marathon. In the waning days of his presidency, Theodore Roosevelt decided that for members of the American military, it would be a 50-mile hike, completed in 20 hours. Late last year Outside contributing editor Tom Vanderbilt decided he wanted to get a sense of what that was like. Turns out, it’s pretty hard.

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