What physiological traits allow yaks to function efficiently in thin air above 10,000 feet?

Significantly larger lungs and hearts relative to body size and efficient blood oxygen carrying capacity

Yaks possess specific physiological adaptations that allow them to thrive in the low-oxygen environment of the alpine areas of Central Asia. Foremost among these are their significantly larger lungs and hearts when compared proportionally to lower-altitude cattle, which directly facilitates more efficient oxygen intake and circulation throughout the body. Furthermore, their blood is noted for being particularly efficient at binding and transporting oxygen molecules. This combined suite of adaptations enables them to perform demanding physical tasks, like traversing steep terrain while carrying heavy loads, with relative ease, an activity that would severely exhaust an unacclimatized human at similar altitudes.