Working out in the great outdoors may produce more psychological benefits than hitting the gym, suggest researchers who say that “green exercise” may boost mood, self-esteem, motivation and enjoyment. But according to a new study, the positive effects of green exercise may have more to do with the color green than with being surrounded by nature.

The study is the first to show that the color green may contribute to the  feel-good benefits of outdoor exercise, the researchers said. The findings were published in the journal Environmental Science and Technology in August.

Researchers at the University of Essex in England had 14 college-age men ride an indoor stationary bicycle for five minutes while watching a video that simulated cycling through a natural environment. The researchers then switched the filter on the video screen from green to black and white for five minutes, and then to red for the same amount of time. The researchers assessed mood immediately after each five-minute cycling session.

The young men felt less fatigued and experienced fewer mood disturbances when they watched the green version of the video during their ride than when they viewed either the black and white or red versions. They also reported feeling more angry when they viewed the red-filtered nature video.

A previous study by the same researchers suggested that as little as five minutes of outdoor exercise produced significant improvements in mood and self-esteem.

Being exposed to shorter-wavelength colors, such as blue and green, evokes feelings of calmness, whereas red and yellow are more stimulating according to the researchers. Lush greenery signaled abundant food and nearby water to early human ancestors, the researchers wrote in their study. As a result, positive feelings toward the color green may have become hardwired into the human brain over the course of evolution, they said.

While the findings are compelling, it's unclear whether the positive vibes arose from the color green itself or from the familiarity of the images shown on the video, said Thomas Plante, a psychologist at Santa Clara University in California, who did not work on the study. “We expect trees to be green, not red or gray. It feels more natural,” Plante said.

Because the study was small and focused on men in their early 20s living in the U.K., it's not clear whether or not the findings would apply to the general population, Plante added.

Nevertheless, the study contributes to a growing body of evidence showing that the environment really matters, Plante said. In his research, Plante has found that where you exercise, whom you exercise with, and even the attractiveness of the people around you might influence your mood and attitude toward exercise.

It's important to pay attention to your environment and your exercise goals — whether you want to feel relaxed or energized, for instance — and find out what helps get you there, whether or not it involves greenery, he said.

Pass it on: Seeing the color green while exercising may make your workout more enjoyable.

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