It’s a familiar feeling for newcomers and tourists: huffing and puffing up a mountain, feeling like reaching the summit is impossible or close to it.
Physical fitness aside, there’s a very real reason people not acclimated to altitude feel physiological changes, like difficulty breathing, when exerting themselves in a new alpine environment.
A continuous supply of oxygen is essential for physical and mental functioning. Your heart, muscles and brain all need better oxygen delivery, especially when they’re working harder. At higher altitudes, there’s less oxygen, resulting in a condition called hypoxia.