Researchers at Cardiff university say safety fears are stopping women from running.
They asked more than one hundred new runners who took part in the World Half Marathon Challenge last year about their motivations for starting.
The main barrier to running was work/life balance with 8 in 10 people saying being too busy prevented them from running.
Having to cross busy roads was also listed as a factor that stopped 12% of people interviewed.
Barriers were different for men and women with men concerned about not achieving targets while some women said they were worried about running in front of others.
Lead researcher Dr Liba Sheeran said:
“The results showed that big events do indeed motivate people to get active and stay active.
“However injuries can be a problem for novice runners with seven out of 10 runners reporting injuries.”
Abbie Audrain, 21, who regularly runs in Cardiff says:
“Its so hard if you have a busy lifestyle, if you’ve got kids and you just don’t have time.
“In the winter it’s cold and you’re running in the dark so you might not feel safe and might not want to do it on your own.”
According to Public Health Wales 56% of adults in Cardiff are considered not of a healthy weight.
NHS Wales say people who are regularly exercise have up to 50% reduced risk of developing diabetes, stroke, heart disease and some cancers.
They say the cost of inactivity in Wales is an estimated £650 million per year.