Some people swear by the treadmill. Others can't wait for the warm weather and the opportunities for outdoor exercise that come with it. But while you might think it comes down to personal preference, there's a small body of research that suggests outdoor exercise might have even more health benefits than a trip to the gym.

The most recent study polled nearly 2,000 active participants in the 2008 Scottish Health Survey and found that outdoor physical activity had a 50 percent greater positive effect on mental health than going to the gym. The researchers, from Glasgow University, found that walking, running, biking and other outdoor activities through green space lowered stress, The Telegraph reported.

It's not the first study to suggest outdoor exercise boosts mental health, but lead researcher Richard Mitchell, Ph.D., told The Telegraph that while the results themselves aren't surprising, the extent to which outdoor exercise beats out indoor activity is. "I wasn't surprised by the findings that exercise in natural environments is good for your mental health, but I was surprised by just how much better it is for your mental health to exercise in a green place like a forest, than in other places like the gym," he said. "The message to doctors, planners and policy makers is that these places need protecting and promoting."

A 2011 study found that outdoor exercise was associated with greater decreases in tension, confusion, anger and depression when compared to indoor activity. And a 2010 study found that even just five minutes of exercise in a green space can improve mood and self-esteem, the BBC reported.

But there are other reasons to take your next sweat session outside. Click through the benefits below, then add your personal reasons for exercising outside in the comments!

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  • Improved Attention And Focus

    A small study from the University of Illinois at Urbana-Champaign found that kids with ADHD were <a href="http://www.ncbi.nlm.nih.gov/pubmed/18725656?ordinalpos=6&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_DefaultReportPanel.Pubmed_RVDocSum" target="_hplink">able to concentrate better after a 20-minute walk in a park</a> rather than a walk through city or neighborhood streets. "What this particular study tells us is that <a href="http://well.blogs.nytimes.com/2008/10/17/a-dose-of-nature-for-attention-problems/" target="_hplink">the physical environment matters</a>," Frances E. Kuo, director of the university's Landscape and Human Health Laboratory and one of the study's co-authors told <em>The New York Times</em>. "We don't know what it is about the park, exactly -- the greenness or lack of buildings -- that seems to improve attention." <em>Flickr photo by <a href="http://www.flickr.com/photos/quacktaculous/3143079032/" target="_hplink">quacktaculous</a></em>

  • Greater Likelihood To Keep Exercising

    While every little bit of exercise counts, let's be honest: most of us could probably afford to do a little bit <em>more</em>. The <a href="http://www.cdc.gov/physicalactivity/everyone/guidelines/adults.html" target="_hplink">2008 Physical Activity Guidelines for Americans</a> recommend the average adult get two hours and 30 minutes of moderate-intensity cardio every week, plus two or more sessions of strength training. It's all too easy to skimp on workouts. However, a 2011 survey found that exercising outdoors is a reinforcing behavior -- the study found that outdoor exercisers "declared a <a href="http://www.ncbi.nlm.nih.gov/pubmed/21291246" target="_hplink">greater intent to repeat the activity</a> at a later date" than gym-goers.

  • Lower Risk Of Being Overweight

    The fresh air, the sunlight, the scenery, the open space -- there's a lot about being outside that can inspire more activity, especially when contrasted to the beckoning couches and screens of indoor spaces. And the extra movement adds up. A 2008 study found that rates of overweight among children who spent more time outside were <a href="http://www.nature.com/ijo/journal/v32/n11/full/ijo2008171a.html" target="_hplink">27 to 41 percent lower than in kids who spent more time indoors</a>.

  • More Energy

    Exercise itself is sure to reinvigorate you when you're feeling sluggish, but fresh air can up the effect. A 2009 study from the University of Rochester found that <a href="http://www.intrinsicmotivation.net/SDT/documents/2010_RyanWeinstenEtAl_JEVP.pdf" target="_hplink">just 20 minutes outside</a> can rev you up <a href="http://www.telegraph.co.uk/science/science-news/7803320/20-minutes-outdoors-as-good-as-cup-of-coffee.html" target="_hplink">as much as a cup of coffee</a>, <em>The Telegraph</em> reported. "Often when we feel depleted we reach for a cup of coffee, but this suggests a better way to get energized is to connect with nature," lead author <a href="http://www.psych.rochester.edu/faculty/ryan/" target="_hplink">Richard M. Ryan, Ph.D.</a>, a professor of psychology at the university told the publication. <em>Flickr photo by <a href="http://www.flickr.com/photos/galant/688642298/" target="_hplink">thebittenword.com</a></em>

  • Faster Healing And Less Pain

    A 2005 study of spinal surgery patients found that patients staying on the sunny side of the hospital reported <a href="http://www.psychosomaticmedicine.org/content/67/1/156.abstract" target="_hplink">less pain, less stress and needed less medication</a> for pain than patients housed on the shady side of the building. Of course, recovering from a surgery will temporarily put a damper on most fitness plans, but if sunlight is the key ingredient, an outdoor workout may just boast some of the same benefits for more minor injuries.

  • Higher Vitamin D Levels

    Taking your workout outside is a great (and free!) way to soak up some additional vitamin D. A 2011 study that found vigorous exercisers had higher levels of vitamin suggested that <a href="http://yourlife.usatoday.com/fitness-food/exercise/story/2011-10-04/Vigorous-exercise-boosts-vitamin-D-while-lowering-heart-risk/50660716/1" target="_hplink">outdoor exercise may be the reason why</a>, <em>USA Today</em> reported. It may be especially helpful for people with a few pounds to lose, according to Everyday Health, since overweight people are almost <a href="http://www.everydayhealth.com/fitness/outdoor-exercise-benefits.aspx" target="_hplink">twice as likely to not get enough vitamin D</a>. <em>Flickr photo by <a href="http://www.flickr.com/photos/wonderlane/4775285017/" target="_hplink">Wonderlane</a></em>

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