Jogging offers the possibility to enjoy some fresh air, nature and the urban scenery and the chance for a good workout of the body and brain. But now researchers have found, after tests conducted on rats, that running alone may be bad when combined with isolation.

The study was launched because of the researcher's desire to see how a stressful activity like running can be good for one's health. Rats forced to live and run alone have less cell brain growth than those who run with others.

Even if the human implications are not clear, "the social environment plays an important role in determining how a basic function like physical activity affects the brain and body," stated Bruce S. McEwen, a professor of neuroendocrinology at The Rockefeller University in New York City.

From the two groups of rats in the study, the ones in groups did better in generating new neurons than those that were isolated. The latter also had a high level of corticosterone, a hormone related to stress.

"For most species, social interaction is very natural. This makes a lot of sense for species which thrive with cooperative activities, like sharing food and cooperative breeding. The stressful component of isolation may be adaptive because it seems to be aversive -- if given a chance, most rats would seek out social situations, especially positive ones -- and so animals are unlikely to stay in an isolated setting if given a chance," said co-author of the study, professor Elizabeth Gould.

It is hard to say if these findings can be applied to humans because rats are motivated to run, whilst people are not motivated to exercise. A clear thing is that moderate exercise stimulates the brain, boosts the memory and the learning capability and too much exercise slows down the production of new brain cells.