Exercising on your own could be causing your brain harm, claim scientists in the US.
Jogging is thought to improve communication between neurons and improve spatial awareness but researchers from Princeton University believe that running alone can bring about a process called neurogenesis, which increases levels of the stress hormone corticosterone and lowers the creation of new brain cells.
However, the research, published in the Nature Neuroscience journal, claims that when jogging with others, this negative process is greatly diminished.
Dr Elizabeth Gould, co-author of the study, wrote: "In the absence of social interaction, a normally beneficial experience can exert a potentially deleterious influence on the brain."
The study has so far only been conducted on rats but researchers are confident the findings will have some bearing on humans.
It is thought the research could also indicate that those who live on their own are more likely to react badly to times of stress than someone in a group environment.