Cross-adaptation is the process of exposing your body to one type of environmental stress to promote adaptations that carry over to another. In the case of heat and altitude, repeated heat exposure triggers cardiovascular changes — increased plasma volume, improved oxygen delivery, enhanced blood flow — that can improve your body’s response to hypoxia. I used this approach while preparing to summit Mount Everest in two weeks door-to-door from my home at sea level. For five months leading up to the climb, I engaged in consistent, structured training under the guidance of Uphill Athlete coaches. For three of those months,…