Can training protect me from altitude sickness, or is it just luck?
How do you train to prevent altitude sickness?
Altitude sickness cannot be trained away with fitness. What decides whether you get it is how fast you ascend and whether your body has time to acclimatize to the lower oxygen pressure, not how strong you are at sea level; a very fit climber can still get it, and excellent shape is no protection.
The full answer, kept up to date: How do you train for altitude sickness?