The Effects of Exercise in Forest and Urban Environments on Sympathetic Nervous Activity of Normal Young Adults
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Forestry and Forest Products Research Institute
, Tsukuba,
Japan
1
Faculty of Engineering, University of Toyama
, Toyama,
Japan
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>> Version of Record - Mar 1, 2006
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The Journal of International Medical Research
2006; 34: 152 159
The Effects of Exercise in Forest and
Urban Environments on Sympathetic
Nervous Activity of Normal Young Adults
M YAMAGUCHI1, M DEGUCHI1 AND Y MIYAZAKI2
In Japan, forest-air bathing and walking
(shinrin-yoku) has been proposed as a
health-facilitating activity in which people
spend a short period of time in a forest
environment. Initially, we examined the
usefulness of salivary amylase activity as
an indicator of an individuals stress levels
in a forest environment. The circadian
rhythm of salivary amylase activity was
measured in healthy young male subjects
under stress-free conditions. The salivary
amylase activity remained relatively
constant throughout the day. Salivary
amylase activity was then measured
before and after walking in both urban
and forest environments using a hand-held
monitor. Our results indicated that (i) the
circadian rhythm fluctuations in salivary
amylase activity were much smaller
than the stressor-induced variations;
(ii) salivary amylase activity was an
excellent indicator of the changes in
sympathetic nervous activity; and (iii) the
forest was a good environment in which
people could experience much less
environment-derived stress.
Introduction
During the 5 million years of human history,
humans evolved to live in forest
environments and it was only around 2000 years
ago that we started living in urban
environments. It is well known that forest
environments have favourable effects on
human physiological functions, and sanatoria
are often built on plateaus in forest
environments. There have been reports that the
forest environment has excellent
physiological effects on patients with allergies or
respiratory diseases.1,2 Factors in the forest
environment that might provide good
physiological effects include the aroma of
the plants,3 various environmental factors
such as temperature, humidity, light
intensity, wind and oxygen concentrations, and
exercise performed within that environment.
In contrast, people who live in an urban
environment often develop diseases such as
chronic fatigue syndrome. Otherwise normal
healthy subjects might develop chronic
fatigue syndrome due to increased fatigue
and stress if they are not appropriately
treated.4 To improve the quality of life of
those who live in cities, it has been suggested
that society develops better methods to
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facilitate and promote healthy activities,
which can be performed in a very short
period of time, are not expensive and
are also enjoyable. In Japan, one such
health-promoting activity is called
shinrin-yoku or forest-air bathing and
walking in which people attempt to spend a
short period of time in a forest environment
performing certain recreational activities
including exercise.5,6 This health-promoting
activity is expected to induce psychological
relaxation in those who experience the
atmosphere of the forest. However, this
theory has not yet been studied scientifically
with regard to the physiological effects of
forest-air bathing and walking on healthy
city-dwellers.
In an attempt to measure quantitatively
the physical and psychological status of
healthy people, a variety of methods have
been studied that have evaluated the
activity of the autonomic nervous system
using electroencephalograms (EEG),
electrocardiograms (ECG), skin conductance
and heart rate. However, these physical
measurements have some limitations as
they not only require the subjects to be
restricted physically, but also require
equipment that is difficult to transport.
Except for heart rate monitoring, these
methods cannot be used in a forest
environment. The measurement of the heart rate
observes the sympathetic nervous activity of
the cardiovascular system and it is strongly
influenced by homeostasis.
In contrast, a method for measuring the
sympathetic nervous system based on a
biochemical marker in saliva has been
investigated.7 Saliva sampling is
noninvasive, making multiple sampling easy
and stress free. It has been suggested that
salivary amylase activity can be a useful
index of plasma noradrenaline levels under
a variety of stressful conditions, since it
appears that increased sympathetic nervous
activity is a major stimulator of amylase
secretion.8,9 We have previously proposed a
new method to quantify salivary amylase
activity and have manufactured a
handheld salivary amylase activity monitor.10,11
We investigated the physiological effects
of forest-air bathing and walking as one
health-promoting activity that could be used
for preventive medicine. In this present
study, we initially examined the circadian
rhythm of salivary amylase activity in
regulated stress-fr (...truncated)