Here's a statistic that will shock you: 67 percent of women have gym memberships that they don't use.

The reason is exactly what you would expect. We have every intention of doing The Right Thing and getting into shape, but we lose motivation within a few short weeks of buying our membership. Regular exercise, it seems, is hard, and many of us have a tendency to stress out about it.

The solution, according to researchers at the the University of Michigan in Ann Arbor, is to lighten up. The study suggests that being more relaxed about physical activity may increase women's motivation to exercise.

The study revealed that “inactive” women – those reporting less than 120 minutes of exercise per week – feel pressured to exercise in order to improve their health or to lose weight, and that anxiety thwarts their desire to be free from pressure during leisure time. Feeling “free” from pressures during our leisure time is a key component of our happiness.

The inactive women in the study believed that for their exercise to mean something, it had to be intense. Again, this worked counter to their need to feel relaxed during their leisure time. All these perceived expectations about what did and did not constitute valid exercise prevented the inactive women from achieving their exercise and weight-loss goals.

"The traditional recommendation we've learned to believe is that we should exercise at a high intensity for at least 30 minutes, for the purpose of losing weight or improving our health. Even though there are newer recommendations that permit lower-intensity activity in shorter durations most people don't know or even believe it," said study co-author Michelle Segar.

"A new understanding of what really motivates women might make an enormous difference in their ability to successfully incorporate physical activity into their daily routine - and have fun doing it."

How can women accomplish this? For one, don't view it as the end of the world if you miss the gym now and again. And don't place exercise as one of your highest priorities – you're likely just setting yourself up to fail. The more relaxed your approach to exercise can remain, the more motivated you will be to actually show up at the gym and use that membership.

The research was published in BMC Public Health.