Women may not have to dedicate as much time as men to staying physically fit and healthy.

A new long-term study of over 400,000 adults in the United States has found that after the same dose of physical activity, female individuals gain greater long-term health benefits than males.

The study, led by experts at the Schmidt Heart Institute in California, tracked participants' health data from 1997 to 2019, comparing physical activity levels with deaths from certain illnesses. In the National Health Interview Survey on which this research is based, participants are asked to identify themselves as either of male or female sex.

Researchers found female participants undertook substantially less physical exercise like brisk walking or cycling each week than male participants. They also did less weight training or core work.

Nevertheless, females who partook in at least some physical activity each week, as opposed to no activity, lowered the risk of dying from any cause by up to 24 percent. For males, regular physical activity was linked to a reduction of just 15 percent all-cause mortality.

The findings suggest that male and female individuals require different doses of regular muscle strengthening and cardio to reap all that exercise can offer to their life expectancy.

In the current study, male participants reached their maximal survival benefit after five hours of cardio per week. For female participants, the same survival benefits were met with just over two hours of moderate to vigorous cardio a week.

In terms of weightlifting or core body work, males reached their peak survival benefit after three sessions a week. Whereas females achieved the same gains from just one session a week.

Researchers are not sure why these sex differences exist, but they have a few ideas. With less of a lean body mass to limit the usual capacity of blood vessels to expand when needed, women could use physical activity to train their cardiovascular system into working that little bit harder.

"In fact," the authors of the latest study write, "physiology studies have demonstrated that female individuals exhibit greater vascular conductance and blood flow during exercise, with female individuals having a higher density of capillaries per unit of skeletal muscle when compared with male individuals."

The findings suggest that public health recommendations for physical exercise should be different depending on the sex.

There is often said to be a gender gap in how much women exercise, but this may not be as big of a problem for public health as some researchers thought.

"Although women seem to do less leisure-time exercise, their mortality risk is more steeply reduced for any given weekly amount or frequency of exercise," physiologist Emmanuel Stamatakis, who was not involved in the study, told Nicola Davis at The Guardian.

"This is not very surprising, considering that such analyses cannot take into account that physical effort women make for a given physical task is higher than in men."

While more studies need to confirm these associations and explore the reasons for why female individuals might need to exercise less, the researchers think it's time to consider the limitations of a "one-size-fits-all" approach to physical health.

"I am hopeful," says cardiologist Christine Albert, "that this pioneering research will motivate women who are not currently engaged in regular physical activity to understand that they are in a position to gain tremendous benefit for each increment of regular exercise they are able to invest in their longer-term health."

The study was published in the Journal of the American College of Cardiology.