Had you ever heard of green exercise before you read the headline above? I certainly hadn't, until I reviewed the abstract for this meta-analysis of 10 British studies encompassing some 1,250 patients that linked outdoor activity in the presence of nature -- anything from a walk in the park to gardening, boating, fishing, biking and even farming -- to improved mental health.

Although there's plenty of evidence that shows how people benefit from a mental health standpoint by doing some kind of physical activity in a natural setting, this study determined how much time it actually takes to reap those benefits. Surprisingly, the optimal mix of nature and activity that had a positive effect on self-esteem didn't amount to much of an investment in time at all. In fact, it was just five minutes.

Of note, when discussing their results, British researchers used the words dose and self-medicate to describe the positive effects activity in a natural setting had on the human psyche, further underscoring the idea that exercise and physical activity should be treated like a drug that must be accurately prescribed -- with the help of a physician or professional trainer -- so the patient can derive the best results.

If physical activity in the presence of nature doesn't work with your schedule, however, consider short-term, high-intensity interval training (HIT) that could maximize your time at the gym and improve your mood with great results.

Environmental Science & Technology March 25, 2010

ScienceDaily May 1, 2010

LiveScience May 2, 2010