If a man and a woman of similar age walk up a steep hill side-by-side, the woman will most likely run out of breath faster than her companion.

This is true whether they are healthy young or older adults, or if both suffer from a chronic lung disease.

That’s because the smaller size of a woman’s lungs, her narrower air passages, and weaker respiratory muscles make breathing during exercise, quite literally, more work for her.

A new study published in the journal Experimental Physiology explains why this is the case.

Prof. Dennis Jensen of McGill’s Department of Kinesiology and Physical Education said “What is novel about our study is that it’s the first to show that because of a woman’s relatively smaller size, when she is exercising, her brain needs to send stronger electrical signals to the respiratory muscles, and specifically the diaphragm, than does a man’s in the same situation.”

“Our study shows that these differences are likely responsible for why women are more short of breath during exercise, even if it is just climbing the stairs.”

Source: Experimental Physiology