Behavior and health experts at the University of Michigan (UM) found that walking outside, in parks or in nature, helps improve conditions such as memory deficit, inattentiveness and other forms of mental fatigue. Even the cold weather is good enough, as the team says that the cold stimulates the brain to be more alert of its surroundings, thus increasing the number of connections it makes and improving attention.

"Interacting with nature can have similar effects as meditating. People don't have to enjoy the walk to get the benefits. We found the same benefits when it was 80 degrees and sunny over the summer as when the temperatures dropped to 25 degrees in January. The only difference was that participants enjoyed the walks more in the spring and summer than in the dead of winter," says Marc Berman, a psychology researcher at UM.

In a test group, some 20 percent of the participants exhibited increased levels of alertness, satisfaction, and mental tranquility after spending one hour in nature. They reported that their levels of stress had decreased significantly, and that they felt more in control of their minds. Stephen Kaplan, another researcher at UM, and his wife Rachel, who is a psychologist at the School of Natural Resources and Environment, found that people who went outside needed three criteria to be satisfied with their lives.

They named the ability to understand and explore as the most important of them, followed by the fact that they needed to feel they made a difference, as well as feeling competent and effective. Kaplan adds that those who adopt a more sedentary lifestyle are very likely to be deprived of these feelings, which makes life increasingly difficult for them.

While struggling to get ahead, both professionally and in their personal lives, people who do not go outside regularly start to lose their focus and become more and more tired, even if they sleep the recommended 8 hours every night.