A recent study published in the International Journal of Psychophysiology1 compared the effects of self-paced walking through an outdoor green environment (GE), an indoor environment while viewing a video of the same outdoor green environment (VGE), and an indoor environment while facing a white wall (IE, Control). Indoor walking occurred on a motorized treadmill.
The researchers hypothesized that outdoor physical activity in nature would promote greater relaxation and positive affect, reduce rumination and physiological stress, and downregulate perceived activation (arousal, energized) more so than the same indoor physical activity. They further hypothesized that indoor physical activity with the VGE would have greater treatment effects than the control.
For study inclusion, participants had to be healthy, between ages 18 and 35, have normal vision and hearing, and not have any neurological disorders. The enrolled 30 study participants were 17 female and 13 male, with a mean age of 24.2 years, and engaged in an average of 192 minutes of physical activity per week.
Participants walked the three treatment conditions in a randomized order. Each walk was approximately six minutes long, with a five-minute rest between the second and third walks. Perceptual and affective status were monitored during the exercise stints. Participants wore an EEG cap and a chest heart rate monitor to measure brain electrical activity and cardiac activity throughout the physical activity treatment protocol.
Heart rate at the beginning of the walks ranged between 90 and 94 bpm, rose to 98 and 102 bpm in the middle of the walks, and further rose to 102 and 105 bpm by the end of the walks. At the end of the walks, attention was increased and highest for GE, intermediate for VGE, and had declined from baseline for the IE control. There was little change from the walks beginning to the end for affective valence. Following the walks, emotional awareness was highest for GE, intermediate for VGE, and lowest for IE control. There was little to no difference between the three walking conditions regarding body awareness.
Following the three different walks, there were distinct differences in the patterns of Theta, Alpha, and Beta brain waves. Theta waves were upregulated in the frontal, parietal, and temporal regions following the GE walk compared to the VGE and IE control walks. Alpha waves were upregulated following the GE walk in the frontal area compared to the VGE and IE control. Beta wave patterns following the walks were similar for GE and the IE control. In contrast, the IE control was downregulated in the frontal region to a greater extent than following the VGE walk.
Based on the results, the authors concluded that the different walking conditions differentially influenced the perceptual, psychological, psychophysiological, and patterns of brain wave activity with the most pronounced effects following the GE walk compared to the IE control and VGE walks. When taken together, the results show different brain mechanisms and responses associated with walking outdoors in a green environment compared to walking indoors, thereby pointing towards a better understanding of why physical activity in an outdoor green environment yields superior health and well-being outcomes.
1Mavrantza, A.M., Bigliassi, M., Calogiuri, G. (2023). Psychophysiological mechanisms underlying the effects of outdoor green and virtual green exercise during self-paced walking. International Journal of Psychophysiology, 184:39-50. https://doi.org/10.1016/j.ijpsycho.2022.12.006
Charles Guy, Emeritus and Courtesy Professor
Department of Environmental Horticulture, University of Florida