What was the subject of your research?

“The relationship between exercise and mental health among over-40s. What made our study special is that we took sitting habits and sleep into account. What happens if you exercise more instead of sitting or sleeping? These factors are important, because if you add up the hours spent exercising, sitting and sleeping, you arrive at 24.”

Rather complex data to obtain!

“Well, we used data from the Erasmus Rotterdam Health Study, the ERGO study. It has been running in Ommoord since the 1990s, among all residents of that neighbourhood. We collect data on exercise, sitting and sleeping using an accelerometer, a kind of Fitbit for scientific research.”

What were the results?

“It is important to take the 24-hour cycle into account, as the effects can vary. Exercising instead of sleeping or sitting was found to relate to fewer depressive symptoms. Sleep duration was found to have less effect on mental health. Sleeping for longer rather than sitting or light physical activity did improve sleep quality. In our studies, we found no positive relationship between exercise and sleep quality. This is surprising, as previous studies did find that exercise benefits sleep quality, although no correction was made for sleep duration in those studies.

“We also observed that people with a healthier brain, with larger brain volumes, continued to exercise better over time, although we did not find that exercise positively affected brain volumes. So, perhaps participants with a less healthy brain should be a specific target group for physical activity interventions. Since these participants seemed to exercise less in the long term.”

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Why is this research important?

“People with mental health problems have a higher risk of other chronic diseases and low quality of life. We also know that this works both ways: people with physical problems are more likely to develop mental problems and vice versa.

“Knowledge of many of the effects of the 24-hour cycle, and the related methods available, is still new. The results can be used to develop guidelines. In the Netherlands, there are still only guidelines regarding exercise, whereas Canada, for example, already has recommendations on sitting, sleeping and exercise.”

What prompted you to choose this research?

“I studied physiotherapy, and there had always been a link with exercise. I also used to play sports fanatically: track and field. I trained for the multi-event. So this subject was a good match.”

Why did you want to do a PhD?

“I wanted to become a researcher. Once you have obtained your master degree, you will have learned all kinds of things but put little of what you learned into practice. I was very curious about the various aspects of research and wanted to develop further in that respect. At the hospital where I now work, I advise researchers on their structure and data analysis and teach about research, so that fascination has remained.”

What was your experience of the PhD programme?

“It was very enjoyable and informative, although it was severely impacted by the pandemic. That was unfortunate. All of the conferences were online. That was not quite what I had envisaged beforehand: travelling and meeting people abroad who were doing the same research. But other than that, it was varied, and I could contribute a lot of my own input. I didn’t enjoy working on my own papers alone five days a week, so I played an active role in data collection, taught where I could and organised seminars. I feel that you learn more from that than from just writing articles.”

I gathered from your acknowledgement that you also have a busy social life.

“True, that also helped me a lot. It keeps you from being focused on your PhD all the time. If I had dinner or something else planned in the evening, I had to leave EMC at five o’clock, for instance. That helped keep working hours within limits. People sometimes seem to think it’s impossible to do a PhD and still enjoy your life, but I wouldn’t have lasted four years had that been the case.”

Did you still have time for sports?

“I grew up with sports being part of my life, and the cover of my thesis features my sporting grandfathers, parents, and brother. Still, it’s hard to get enough exercise when you have such a sedentary job. That does feel wrong: writing that sitting is very bad for you, yet spending a few years mostly sitting. Fortunately, I walked a lot during the pandemic; I also used the Ommetjes app, which encourages you to go on regular walks, together with colleagues.”

Promotie Stijn Weterings _Levien Willemse

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