Elizabeth Dunn, director of the Happy Lab at the University of British Columbia, says that exercise isn't just good for the body, it can have major benefits for your state of mind.

In the latest installment of The Early Edition's summer series, The Pursuit of Happiness, Dunn says that the link between exercise and happiness are well established — but there are a few reasons why people don't get off their duffs and work out.

"There's now dozens and dozens of studies showing that after people exercise, they get a boost of happiness for about two to four hours," she said. "Over time, there's some evidence that exercising regularly can increase your chronic levels of happiness."

So why don't we exercise more? Dunn says there are a few factors that keep us away from the gym or the yoga studio, and those hurt our health and our happiness.

Look for a good space

Dunn said one thing that's very important is that people need to be able to exercise comfortably if they expect to keep at it.

She gives the example of how some gyms are poorly designed, stuffy and just generally unpleasant to be in for any period of time.

"If you're feeling like working out isn't giving you much of a happiness benefit, then it's worth thinking if there's a more comfortable environment to work out so you can unleash those happiness benefits," she said.

Dunn also says the same is true for outdoor exercisers. It can be hard to stay motivated and keep to an exercise routine if it's freezing cold or blisteringly hot.

To be (fit), or not to be (fit)

Dunn also identifies a key moment for anyone looking to get fit that often turns into a barrier: the time you spend contemplating whether or not you want to exercise.

Dunn says that often, this time is contemplating the effort and unpleasantness of starting a workout, when really, it's better to think about the positive feelings you get finishing a workout.

Dunn and graduate student Matt Ruby did some research into this phenomenon by looking into people who do a wide range of exercises.

"We looked at how people expected to feel when they were working out and how they actually felt after working out," she said. "What we saw was people … significantly underestimated just how much they would enjoy working out."

Dunn says if this is a problem for you, you should consider making changes to the start of your workout so it becomes more enjoyable.