Working out in the park may have more psychological benefits than hitting the gym, according to researchers who found that "green exercise" enhances mood, self-esteem, motivation and enjoyment.

However, researchers noted that the positive effects have more to do with the color green than with being surrounded by nature.

Researchers said that the latest finding, published in the journal Environmental Science and Technology, is the first to show that the color green may contribute to the mental benefits of exercising in the great outdoors.

British researchers at the University of Essex conducted a small study of 14 college-age men who were asked to ride an indoor stationary bicycle for five minutes while watching a video that simulated cycling though a natural environment.

Researchers had then switched the filter of the video screen from green to black and then white for five minutes. Afterwards, they asked participants to cycle for five minutes looking at the screen through a red filter.

Researchers had evaluated the mood immediately after each five-minute cycling sessions.

The results from the study showed that participants felt less fatigued and experienced fewer mood disturbances when they watched the video through the green filter compared to when they viewed the video through the other color filters.

Researchers noted that the men reported feeling more angry when they viewed the red-filtered nature video.

In the past, the same group of researchers found that as little as five minutes of outdoor exercise was enough to produce significant improvements in mood and self-esteem.

Researchers said that the latest findings suggest that being exposed to shorter-wavelength colors like blue and green evokes feelings of calmness whereas longer-wavelength colors like red and yellow are more stimulating. Researchers hypothesized that the latest findings may be the result of evolution. They explained that because lush greenery indicated abundant food and nearby water to early human ancestors, positive feelings toward the color green may have become hardwired into the human brain over the course of evolution.