While both sexes have the capacity for phenomenal athletic achievements, researchers have found that breathing during difficult exercise may be harder for women as compared to men.

The study suggests one possible way sex could affect exercise dynamics and potentially also contribute to differences in how men and women experience airway disorders such as asthma and chronic obstructive pulmonary disease (COPD).

"The amount of work the respiratory muscles have to do to breathe a given volume is greater in women. It is thought that this is due to women having smaller airways than men, which causes the airflow resistance to be higher," said study researcher Paolo Dominelli from the University of Waterloo in Canada.

For the findings published in the FASEB Journal, the research team recruited six men and five women to perform two maximal exercise tests, in which participants gradually increased their level of exertion on a stationary cycle until they were exercising as hard as they could.

Participants breathed through a mouthpiece attached to a large bag. During one session, the bag was filled with normal room air.

During the other, the bag was filled with a mixture of oxygen and helium. Each bag contained the same amount of oxygen, and participants were not told which mixture they were breathing on which day.

A small tube was inserted into the participants' nose and throat during the tests to monitor the pressure inside the oesophagus.

This procedure allows researchers to measure the amount of work required to breathe. When the bag contained the helium mixture, the results showed no differences in the work of breathing between men and women.

When it contained room air, breathing required significantly more work for women than men, the researchers said.

The researchers cautioned that the differences observed in the study relate to size and sex and that there is great variability in airway size among different individuals.