“Shinrin-yoku”, which can be defined as “taking in the forest atmosphere or forest bathing”, has been receiving increasing attention in Japan in recent years for its capacity to provide relaxation and reduce stress. Since 2004, the authors of this paper have been involved in an investigation designed to ascertain the physiological effects of “Shinrin-yoku” within the framework of the “Therapeutic Effects of Forests” project. We have conducted physiological experiments, both in actual forests and in the laboratory, to elucidate the physiological effects on individuals of exposure to the total environment of forests or to only certain elements of this environment, such as the odor of wood, the sound of running stream water, and the scenery of the forest. We have obtained physiological measurements of central nervous activity, autonomic nervous activity, and biomarkers reflecting stress response that can be applied in this line of approach. Using these measurements, we have summarized the separate elements of forests in terms of the five senses. We have also reviewed a selection of field studies and introduced a number of results from ongoing projects as well as those from early studies. Future perspectives are also discussed.

The present study investigated the well-being effects of short-term forest walking and viewing (“forest bathing”). The hypothesis in our study was that both environment (forest vs. urban) and activity (walking and viewing) would influence psychological outcomes. An additional aim was to enhance basic research using several psychological methods. We conducted the experiments using 45 respondents in four areas of Japan from August to September, 2011. The hypothesis in our study was supported, because significant interaction terms between the environment and activity were confirmed regarding the Profile of Mood States (POMS) indexes, Restorative Outcome Scale (ROS) and Subjective Vitality Scale (SVS). No statistical differences between the two experimental groups in any of the ten scales were found before the experiment. However, feelings of vigor and positive effects, as well as feelings of subjective recovery and vitality were stronger in the forest environment than in the urban environment.

The physiological effects of “Shinrin-yoku” (taking in the atmosphere of the forest) were examined by investigating blood pressure, pulse rate, heart rate variability (HRV), salivary cortisol concentration, and immunoglobulin A concentration in saliva. Subjective feelings of being “comfortable”, “calm”, and “refreshed” were also assessed by questionnaire. The subjects were 12 male university students aged from 21 to 23 (mean±SD: 22.0±1.0). The physiological measurements were conducted six times, i.e., in the morning and evening before meals at the place of accommodation, before and after the subjects walked a predetermined course in the forest and city areas for 15 minutes, and before and after they sat still on a chair watching the scenery in the respective areas for 15 minutes. The findings were as follows. In the forest area compared to the city area, 1) blood pressure and pulse rate were significantly lower, and 2) the power of the HF component of the HRV tended to be higher and LF/(LF+HF) tended to be lower. Also, 3) salivary cortisol concentration was significantly lower in the forest area. These physiological responses suggest that sympathetic nervous activity was suppressed and parasympathetic nervous activity was enhanced in the forest area, and that “Shinrin-yoku” reduced stress levels. In the subjective evaluation, 4) “comfortable”, “calm”, and “refreshed” feelings were significantly higher in the forest area. The present study has, by conducting physiological investigations with subjective evaluations as supporting evidence, demonstrated the relaxing and stress-relieving effects of “Shinrin-yoku”.

To clarify the visual effects of room interior with wooden materials on humans, pulse rate, blood pressure, and brain activity were measured while the subjects were exposed to visual stimuli using actual-size model rooms. The wood ratios (the ratio of the area covered with wooden material to the whole area of the ceiling, walls, and floor) of the rooms were 0%, 45%, and 90%. Subjective evaluation was also conducted. In the 0% room, diastolic blood pressure decreased significantly, but the observed change in the autonomic nervous activity was relatively small. In the 45% room, a significant decrease in the diastolic blood pressure and a significant increase in pulse rate were observed. This room tended to have the highest scores in subjective “comfortable” feeling. The 90% room caused significant and large decreases in systolic blood pressure and diastolic blood pressure at the beginning of the test, but the large coverage of wood appeared to cause a rapid decrease in brain activity and an increase in pulse rate. The present study demonstrated that a difference in wood ratio in the interior caused different physiological responses, especially in the autonomic nervous activity, by using actual-size rooms for the first time.

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