When fit young men exercise at a high altitude (like on a mountain), their bodies release more sugar, fat, and stress hormones into the blood than when they exercise at sea level—this means their body switches how it uses energy when there’s less oxygen around.

When fit young men exercise at a high altitude (like on a mountain), their body drops insulin levels way more than when they exercise at sea level—and once they stop exercising, insulin shoots back up quickly.

When healthy young men exercise hard at high altitudes (where there's less oxygen), their bodies release certain hormones that help break down fat and make more sugar for energy.