If at sea level you can maintain walking up a 3-5% grade at 50% HR, or around 25-30% VO2max, or maybe around 120-130bpm, then you should not have a problem at all.

At 14,000 feet your body needs 60-70% of VO2max to accomplish the same level, or roughly 75-80% of MHR. That's doable for at least a couple hours of walk/rest/walk/rest. No problem.

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