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Women experience greater shortness of breath than men during exercise because their breathing muscles show greater electrical activation.  

Researchers have long known that women experience greater shortness of breath during physical activity than men of a similar age. This is true in healthy young and older adults, as well as in patients with chronic heart and lung disease.

Researchers said the latest study is the fist to explain why this happens.

"Our study uniquely showed that sex differences in activity-related breathlessness could be explained by the awareness of greater electrical activation of the respiratory muscles - specifically the diaphragm - needed to achieve any given ventilation during exercise in healthy young women compared to men," lead researcher Dr. Dennis Jensen of McGill University in Canada said in a news release.

"Our findings indicated that greater electrical activation of the respiratory muscles during exercise in women is needed to compensate for their biologically smaller lungs, airways and breathing muscles," Jensen added.

Researchers said the latest findings could be used to help identify new treatments to relieve the symptoms of breathlessness and improve exercise capacity for groups such as the elderly and patients with chronic heart and lung disease.

"50 healthy, non-smoking men and women aged 20-40 years completed a maximum exercise test on a stationary bicycle. During exercise, we monitored the participants cardiovascular, metabolic and ventilatory responses to exercise using computerized equipment," Jensen said.

"At regular intervals during exercise, participants rated the intensity of their breathlessness using a 10-point scale. Using a multipair electrode catheter placed in the participants' oesophagus, we also recorded the electromyogram of the diaphragm (an index of the drive to breathe that presumably originates in the central nervous system) throughout exercise," Jensen added. "These measurements were then analyzed and compared between men and women."

The findings were published in the journal Experimental Physiology.