Here's the how: Sharok Toker and Michal Biron assessed employed visitors to a medical centre on three occasions spanning on average 40 months. They ended up with 1,632 participants from a range of occupations with a mean age of 47, mainly (70%) male. At each time point participants recorded levels of burnout, in terms of fatigue, cognitive weariness ("I have difficulty concentrating") and emotional exhaustion, as well as completing the depression scale of a patient-oriented clinical instrument. Participants also reported the volume of strenuous exercise they conducted within a typical week in the last month.
The what is as described: an increase in burnout from time one to time two predicted an increase in depression from time two to time three, even controlling for time two depression (that is, depression at the time of the burnout uptick). The same effect was found for depression on subsequent burnout. Why? These concepts are understood as related but distinct, with burnout reflecting strain due to the quality of the social situation at work whereas depression is a global state that involves a range of symptoms and an intense experience of sadness or diminished pleasure. Both however make demands on psychological and energetic resources, and this study's results bear out its expectations that a drain on these resources from one origin - such as a harried workplace - can lay the groundwork for other problems.
How about physical exercise? Toker and Biron hypothesised several reasons why it might act as a bulwark against this spiral. Exercise activates systems that can have physical outcomes like improving sleep and even damping down the physical consequences of sustained stress. It can also produce psychological benefits such as better body image and mood states. Moreover, it can be a useful way to take our mind off things, distracting from specific concerns (such as work challenges) or global cognitions (negative thoughts). Toker and Biron found that the more exercise you do, the milder the effect of earlier burnout/depression upon the other variable at a later time point, to the point of obliterating the effect for high doses of exercise. They conclude that, as well as considering the larger links between job burnout and global depression, employers should recognise the benefits of exercise “as an important means of preventing the build-up of work-related or general distress.”