A group of researchers in 2019 conducted a pilot study looking at the psychological outcomes measured from thirty-eight participants before and after three conditions: a 50 min walk on a forest path, a 50 min walk along a busy road, and a period of activities of daily living. Current estimates suggest that 20% of adults experience a mental illness in a given year, and 4.6% experience a serious mental illness in 2018.
In this study they recruited undergraduate and graduate students and employees from Northwestern University and residents of Evanston, IL, USA and nearby communities. Potential participants were screened against the following inclusion criteria: between the ages of 18–35 years, fluent in English, and healthy as assessed by their readiness to engage in moderate physical activity, which was assessed via the Physical Activity Readiness Questionnaire. Women who were pregnant or breastfeeding were excluded. Participants completed a brief survey to assess their psychological and cognitive states. Subsequently, each participant completed two series of three 50 min walks in a specified location, separated by a nine-day washout period between series. Each participant completed a series of three 50 min walks along a busy road and one series in a forest preserve, but the sequence or Forest to Road for walk locations was assigned randomly.
They then reported on data collected on days 1, 8, 15, 22, and 29 of the study. The walks taken on days 8 and 22 are the first walks that each participant took in each location and thereby provided the most direct comparison to prior studies. Prior to each walk participants came to the laboratory, where they completed the survey to assess their psychological and cognitive state and also engaged in measurement of physiological outcomes. Participants were then driven to the start site for the walk; after the walk they were driven back to the laboratory where they repeated the survey in order to assess their post-walk psychological and cognitive state.
After completing the pre-walk survey, one to four participants were driven from the laboratory to the starting point for the walks; a drive of approximately 10 km (~20 min; one-way). Participants were instructed to walk the assigned route for 25 min and then return by the same route. All participants walked alone. If multiple participants had been driven to the walk site together, their start times were staggered so they were not walking in pairs or groups. Participants did not carry cell phones or other mobile devices during the walks, and they were provided a stopwatch to time their walks. Participants controlled their own walking pace, were discouraged from running, and were asked not to sit down at any point, but simply to walk continuously. After a nine-day washout period, participants walked in the other location. On days with no walks, participants came to the laboratory and completed the survey but did not go for a study-related walk. Instead, participants left the laboratory to go about their activities of daily living for 2 hours. Upon returning to the laboratory, participants repeated the survey.
Before and after each walk or an ADL control session, participants completed a brief survey that contained psychological scales and a test of attention and working memory. What they found was that moderate-intensity walking in a forested environment had a positive impact on psychological health. These findings support the long-known effects of moderate-intensity physical activity on mental health and suggest that completing physical activity in greenspaces amplifies beneficial acute psychological responses. Indeed, these results echo a rich literature extolling the mental and physical health benefits of physical activity, which consistently finds that, whenever and wherever possible, 30–50 min of light exercise can buffer against the wear-and-tear of daily life. The results also support the growing literature that activity in greenspace yields greater improvements in mental health than does activity completed indoors or in a built urban environment.
Koselka, Elizabeth P D et al. “Walking Green: Developing an Evidence Base for Nature Prescriptions.” International journal of environmental research and public health vol. 16,22 4338. 7 Nov. 2019, doi:10.3390/ijerph16224338