Sabine Schaefer, a researcher at the Max Planck Institute for Human Development in Germany, recently looked at the effect of walking on working memory. Your mother may have warned you not to walk and chew gum at the same time, but when Schaefer compared the performance of both children and young adults on a standard test of working memory when they were sitting with when they were walking, her results contradicted mom's advice. The British Psychological Society's Research Digest sums up the research results:
The headline finding was that the working memory performance of both age groups improved when walking at their chosen speed compared with when sitting or walking at a fixed speed set by the researchers. This was especially the case for more difficult versions of the working memory task, and was more pronounced among the children than the adults. So, this would appear to be clear case of mental performance actually being superior in a dual-task situation.
Or in other words, rather than assume that walking while thinking splits your mental and physical resources, leaving less to devote to each, the scientists actually found "an increase in arousal or activation associated with physical activity… which then can be invested into the cognition," according to the paper reporting the research. Walking increases your resources of energy, which you can then invest in thinking.
Why didn't walking at "fixed speed" have the same effect on working memory as walking at the subjects' preferred pace? The scientists speculate that, "walking at the fixed speed, which was considerably slower than the preferred speed in both age groups, might simply not have been fast enough to increase arousal sufficiently to achieve an effect," or that the need to "pay some attention to adjusting one's walking speed to the speed of the treadmill" interfered with the main memory task.
Of course, not every mental activity can or should be performed while walking, but this new research reinforces anecdotal evidence and other research findings that suggest being too tightly chained to our desks is bad for our minds as well as our physical health. Science shows we often have creative breakthrough when our minds are disengaged from the problem we're wrestling with, hence the common experience of getting great ideas while relaxing in the shower.
Getting up for a walk or a jog is another way to achieve this sort of head space — after all, it worked for Einstein and Charles Darwin. (Beer, apparently, also helps.) Other studies have demonstrated that even five minutes outside in nature can improve your mood and self-esteem.