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Assessing the Effects of Nature on Physiological States Using Wearable Technologies

International Journal of

Environmental Research

and Public Health

Article

Assessing the Effects of Nature on Physiological States Using

Wearable Technologies

Dannie Fu 1, Natalia Incio Serra 2, Hubert Mansion 3, Emilia Tamko Mansion 3 and Stefanie Blain-Moraes 2,*

1 Department of Biomedical Engineering, McGill University, Montreal, QC H3A 2B4, Canada;

dannie.fu@mail.mcgill.ca

2 School of Physical & Occupational Therapy, McGill University, Montreal, QC H3G 2M1, Canada;

natalia.incioserra@mail.mcgill.ca

3 L’Université Dans la Nature, Montreal, QC H1V 1H6, Canada; hubert.tlmvdn@gmail.com (H.M.);

emilia@unature.org (E.T.M.)

* Correspondence: stefanie.blain-moraes@mcgill.ca

Citation: Fu, D.; Serra, N.I.; Mansion,

H.; Mansion, E.T.; Blain-Moraes, S.

Assessing the Effects of Nature on

Physiological States Using Wearable

Technologies. Int. J. Environ. Res.

Public Health 2022, 19, 1231. https://

doi.org/10.3390/ijerph19031231

Academic Editor: Paul B. Tchounwou

Received: 7 December 2021

Accepted: 20 January 2022

Published: 22 January 2022

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4.0/).

Abstract: Nature therapy and forest bathing (FB) have been shown to have quantiﬁable positive

effects on human health, but the physiological effects of a guided interactive nature activity remain

unexplored. Autonomic nervous system responses to a guided nature walk (Nature Break) were

assessed through the continuous measurement of the electrodermal activity (EDA), ﬁngertip temper-

ature, and heart rate (HR) of n = 48 participants, using a wearable sensor. Psychological distress was

assessed before and after the activity using the Proﬁle of Mood States (POMS) for n = 38 (24 females,

14 males, mean age = 43.55 ± 11.61 years) participants. The negative dimensions of POMS decreased

and the positive (vigor) dimensions increased following a Nature Break. Signiﬁcant differences were

found across all of the physiological features, with some differences occurring between the morning

and afternoon groups and between different days. The participants’ mean HR decreased throughout

the Nature Break. Our results suggest that interactive nature activities have positive psychological

beneﬁts and demonstrate the feasibility of using wearable sensors to monitor physiological responses

in a naturalistic forest bathing activity.

Keywords: forest bathing; autonomic nervous system; proﬁle of mood states; wearable technology;

forest therapy

1. Introduction

In 2018, Northern America was the most urbanized geographic region in the world

with 82% of its population living in urban areas. Globally, 55% of the world’s population

was living in urban areas in 2018 with this number projected to reach 68% by 2050 [1]. Rapid

urbanization poses many socio-economic, environmental, and psychological challenges,

such as increased levels of crime, air and water pollution, and the psychological stressors

that are associated with higher levels of density and diversity of cities. The environmental

particulate matter that is associated with decreased air quality may be related to cardiovas-

cular deaths and asthma and noise exposure may be associated with hearing impairment,

hypertension, and ischemic heart disease [2].

Over the past few decades, there has been growing interest surrounding the impacts

of natural environments on human health and well-being. In 1982, the term shinrin-yoku,

also known as forest bathing (FB), was coined by the Ministry of Agriculture, Forestry

and Fisheries of Japan to describe the practice of immersing oneself in a forest environ-

ment using all ﬁve senses in order to improve one’s mental and physical health [3–5].

The accumulating evidence has demonstrated that exposure to nature has quantiﬁable

positive effects on the psychological and physiological health of human beings [3,5–7]. In

particular, the act of immersing oneself in a forest has been associated with decreased blood

pressure in comparison to immersion in urban environments [4,8]; signiﬁcant decreases in

Int. J. Environ. Res. Public Health 2022, 19, 1231. https://doi.org/10.3390/ijerph19031231

https://www.mdpi.com/journal/ijerph

Int. J. Environ. Res. Public Health 2022, 19, 1231

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physiological biomarkers of stress such as salivary cortisol and alpha-amylase [9,10]; and

improvements in psychological measures of tension, anger, fatigue, anxiety, confusion, and

depression [4,11–13].

Research in this ﬁeld has been translated directly into various health initiatives, as

FB and nature walks have become increasingly popular as methods of promoting active

lifestyles and improving overall wellness [14] and have started being prescribed by doctors

and recommended by federal, provincial and local associations. On the global scale, Health

Parks Healthy People (HPHP) is a movement that is working alongside many large groups,

such as the National Park Service in the United States and Ontario Parks in Canada, to

advocate the physical and mental beneﬁts of nature. For example, Mood Walks is a program

led by the Canadian Mental Health Association, Ontario, that promotes nature walks to

improve physical and mental health.

Research to date has provided psychological and physiological evidence regarding the

positive impacts of FB and nature walks. To date, most physiological studies have primarily

assessed the effects of natural environments on cardiovascular measures, such as heart

rate, heart rate variability (HRV), and blood pressure [3–5,12,15–18]; neuroendocrine or

metabolic indexes, such as cortisol and adrenaline [5,19–21]; or immune and inﬂammatory

indexes, such as natural killer (NK) cells and tumor necrosis factor-alpha (TNF-α) [5,22–24].

Few studies have assessed the physiological effects of natural environments on electro-

dermal activity (EDA) or peripheral skin temperature, which directly reﬂect sympathetic

and parasympathetic nervous system activity and have been reliably connected to an

individual’s mental and emotional state [25–28].

Further, only a few studies have investigated purposeful engagement with the envi-

ronment during a nature therapy session or walking session [29–31]. Duvall (2013) looked

at the impact of cognitive engagement strategies, such as focusing on a sense (e.g., noticing

different sounds) or taking on a new role (e.g., imagining they are looking for inspiration

as an artist), on well-being and perception of the environment during outdoor walking

sessions. They found that only those in the engagement condition became more satisﬁed

with multiple aspects in their walking environment, such as general appearance, nature

sounds, and the variety of things to look at [30]. Furthermore, the engagement condition

was associated with self-reported signiﬁcant increases in attention and decreased feelings

of frustration [29,30]. Similarly, Korpela et al. (2017) found that focused attention on

interactions with nature was associated with mood enhancement and self-reported positive

restoration [31].

Building upon these studies, we aimed to assess the in-situ effects of a 120-min guided

Nature Break activity that encouraged participants to deliberately engage with their envi-

ronment. In order to characterize the effects of this activity on an individual’s physiological

state, we recorded three signals that reﬂect sympathetic and parasympathetic activity:

EDA, ﬁngertip temperature, and HR. We monitored these signals using a wearable sensor

and mobile application in order to obtain moment-by-moment measures of physiological

reactions that could be correlated with the speciﬁc activities in the forest. We also assessed

the effect of the Nature Break activity on participants’ self-reported mood states using the

POMS questionnaire. We hypothesized that a Nature Break would psychologically reduce

negative affect and increase positive affect, in accordance with previous studies. We also

hypothesized that the different activities in the forest would induce distinct and dissociable

physiological response proﬁles in Nature Break participants.

2. Materials and Methods

2.1. Description of the Nature Break Activity

2.1.1. L’Université dans la Nature

L’Université dans la Nature (UdN) is a non-proﬁt organization that is located in

Montreal, Canada. UdN’s vision is to create stronger and more sustainable communities

and economies through solutions that are inspired by nature. The mission of L’UdN is to

equip the decision-makers of today and tomorrow (e.g., university students) with reliable

Int. J. Environ. Res. Public Health 2022, 19, 1231

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and sustainable methods of decision-making, stimulating creativity and innovation, and

preventing stress through encounters with nature.

2.1.2. Nature Break

Nature Break is a guided immersion event in the forest that lasts approximately

120 min. The guide educates the participants about the neuroscientiﬁc ﬁndings of the

impacts of nature on human health and also aims to catalyze a personal connection with

nature. This activity seeks to generate awareness of the changes in mental and physiological

state that are induced by anchoring the reasons for these changes in a concrete experience

with measurable effects.

Nature Break was modelled on scientiﬁc research conducted in Scandinavia, the

United States and Southeast Asia [32–34]. This non-sporting and non-doctrinal activity is

framed by sensory exercises and a dissemination of scientiﬁc knowledge about the beneﬁts

of nature that are within everyone’s reach.

Nature Break is comprised of ﬁve principal segments in the forest, which incorporate

various themes surrounding the ﬁve senses (e.g., touch, sight, hearing, etc.). Individuals

are invited to perform exercises that stimulate their senses in each segment; all segments

were designed to guide and stimulate the participant’s perception and sensory experience

of the forest. See Table 1 for a detailed description of the segments and exercises.

Table 1. Description of segments in the Nature Break activity.

Forest Activity Segment

1: Pre-forest

2: Sitting on stumps

3: Breathing

4: Old tree

5: Walking barefoot

6: Ferns

7: Pine tree refuge

8: Post-forest

Description

The participants ﬁll out pre-forest POMS and don the wearable sensor.

The UdN guide invites the participants to understand the course of

time in forests and invites comparisons with the speed of life in the city.

The participants are standing. The UdN guide invites them to do a US

Army breathing exercise and to focus on smells. The guide explains

what scientists have found about certain particles emitted by trees and

their healing beneﬁts. S/he will also discuss facts about the air that is

breathed in the city. The participants will practice a breathing exercise

that they can repeat on a daily basis.

The participants are invited to lie down directly on the ground. The

UdN guide explains the scientiﬁc discoveries that are related to the

body’s contact with the ground. The participants practice an exercise

that they can repeat on a daily basis. The participants are also invited

to grab a handful of dirt and to observe and smell the contents.

The participants are invited to remove their shoes and socks for the

duration of the walk to the next stop.

The participants are invited to observe and listen to their immediate

environment. The UdN guide explains Dr. Ulrich’s “View through the

window” study [35] and the uses of nature in hospitals since this

discovery. The participants practice an exercise that they can repeat on

a daily basis.

The guide explains the discoveries that demonstrate the positive

impact of nature on mental health and invites participants to ﬁnd their

own refuge in this clearing. They stay here for a couple of minutes and

then meet the guide. The participants are invited to taste some resin

from the pine trees.

the guides lead a group discussion about the participants’ forest

experience. The participants ﬁll out post-forest POMS.

Length (min.)

~10–20

~10–15

~20

~20–30

~10–15

~15–20

2.2. Participants

A total of 58 individuals participated voluntarily in this study through UdN’s Nature

Break program. Thirty-eight participants from two days of data collection completed

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the POMS questionnaire (n = 38, 24 females, 14 males, mean age = 43.55 ± 11.61 years);

and 48 participants across all of the days of the data collection period provided their

physiological data for analysis. All of the participants were ﬂuent in English and French.

2.3. Study Site

The study was conducted in the autumn season on a private woodlot in Barnston Ouest,

Quebec, which is located in the Great Lakes–St. Lawrence forest region in Canada. This

forest region is characterized by a mix of deciduous and coniferous trees, including red pine

(Pinus resinosa), eastern white pine (Pinus strobus), and yellow birch (Betula alleghaniensis), as

well as some boreal species, such as the American beech (Fagus grandifolia) (Information

from https://www.sfmcanada.org/en/canada-s-forests1 accessed on 26 January 2021. The

private woodlot was located away from trafﬁc and the city. The Nature Break activity took

place in the forest where participants were immersed in the forest setting and could not

hear or see trafﬁc or buildings. Meteorological data was collected from a nearby station in

Coaticook (latitude: 45◦09 00.000 N, longitude: 71◦48 00.000 W).

2.4. Procedure

The study was conducted on three days during the last two weeks of September, 2020.

The maximum and minimum temperatures were 11 ◦C and −3.1 ◦C, 26.5 ◦C and 12.5 ◦C,

and 23.8 ◦C and 17.1 ◦C for days 1 through 3, respectively. Each day accommodated a

group of ten participants in the morning, followed by another group of ten participants in

the afternoon. Upon arrival at the site, participants were greeted by the co-founder of the

Nature Break program who gave them a brief overview of the study and instructed them to

ﬁll out both the informed consent form and the POMS for the pre-forest assessment of their

psychological state. Subsequently, we introduced the physiological monitoring technology

to the participants, showing them how to wear the sensor, what data was being recorded,

and how to use the smartphone application. Participants then donned the physiological

sensor on their dominant hand and kept the paired smartphone in their purse, pocket, or

held in their hand for the remainder of Nature Break. Baseline physiological measures were

obtained from when the participant put the sensor on to just prior to starting the activity.

We brieﬂy reiterated the goals and content of the Nature Break and the study to

the group of participants, prior to proceeding to the forest. The Nature Break activity

consisted of eight segments (Table 1). After the activities in the forest, the participants

were led to a ﬁeld where they ﬁlled out the POMS for the post-forest assessment of their

psychological state. The Nature Break’s guides led a discussion with the entire group about

their experiences in the forest.

2.5. Data Collection

2.5.1. Psychological Measurements

The Proﬁle of Mood States (POMS) was used as a measure of psychological distress.

The original tool consists of 30 adjectives which collectively measure six effective dimen-

sions: tension-anxiety (T), depression-dejection (D), anger-hostility (A), fatigue-inertia

(F), vigor-activity (V), and confusion-bewilderment (C). Each adjective is rated using a

5-point scale from 0 to 4. Our study uses an adapted version of the POMS, consisting of

18 adjectives [36].

2.5.2. Physiological Measurements

The autonomic nervous system (ANS) is composed of the parasympathetic and sym-

pathetic branches, otherwise known as the “rest or digest” and “ﬁght or ﬂight” systems.

Typically, excitation of the sympathetic nervous system and inhibition of the parasympa-

thetic nervous system occurs in response to states such as anxiety and stress [37], while

the opposite may occur during states of relaxation [38,39]. Changes in autonomic nervous

system (ANS) signals, such as EDA, HR, and skin temperature, are connected to internal

emotional or mental states [40,41].

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Three physiological signals reﬂecting ANS activity were collected from a wearable

device called the Triple-Physiology Sensor (TPS) (Thought Technology Ltd.©, Montreal,

Quebec, Canada). The TPS is worn on the ﬁngertip and secured with Velcro wrap. It

collects three physiological signals: (1) electrodermal activity (EDA), (2) skin temperature,

and (3) blood volume pulse (BVP), which is used to derive heart rate (HR) and heart rate

variability (HRV).

Electrodermal Activity (EDA)

Electrodermal activity (EDA) reﬂects sympathetic innervation of the ANS and has

long been used as an indicator of emotional arousal to external or internal stimuli, such

as emotional thoughts, memory recall, or novel, startling, or threatening stimuli [38,42].

These stimuli may evoke electrodermal reactions (EDRs) which appear as transient peaks

in the EDA signal.

Fingertip Skin Temperature

Fingertip temperature is often used as a measure of sympathetic activity but it is

dependent on the subject’s body temperature. When the initial ﬁngertip temperature is

above 33.2 ◦C, sympathetic innervation induces vasoconstriction causing less heat to be

radiated from the surface; however, below this temperature, vasoconstriction is not possible

and vasodilation occurs in response to the same sympathetic stimulus [38,42]. Fingertip

temperature has been shown to decrease in response to stimuli such as sudden noises,

fear, pain, and mental stimulation (such as motor imagery), and to increase during mental

relaxation [38,42,43].

Heart Rate (HR)

The heart is innervated by both the sympathetic and parasympathetic branches of the

ANS. Heart rate has been shown to decrease when an individual’s attention is focused

on the external environment and when sensory information gathering is high, it has been

shown to increase during internal focus or when the sensory input is dampened [38].

Higher HR is also associated with elevated states of stress and anxiety [44,45].

2.6. Data Analysis

The difference in psychological and physiological measures was assessed before and

after the Nature Break activity. Changes in the physiological signals were also assessed

across all of the segments of the activity that took place within the forest.

2.6.1. Psychological Measures Analysis

For the pre-post Nature Break psychological assessment, the mean POMS score for

each dimension was taken across all participants (n = 38). The pre-post signiﬁcance was

computed using Wilcoxon signed-rank paired t-tests. The results were tested against the

Bonferroni-Holm adjusted alpha levels of 0.05 and 0.01.

2.6.2. Physiological Measures Analysis

First, each of the ANS signals were pre-processed in order to remove non-physiological

artifacts by applying smoothing ﬁlters (1D median ﬁlter, moving average ﬁlter), cubic

spline interpolation, and modality speciﬁc ﬁlters. A one Euro ﬁlter was applied to the EDA

signal; an exponential decay ﬁlter was applied to the skin temperature signal; and a cubic

smoothing spline was applied to the HR signals [46].

The signals were then segmented by forest activity and the following features were

extracted [47]: (1) The standard deviation of the slopes of the EDA was used to determine

the presence or absence of EDRs; (2) The median of the slopes of the skin temperature

was used to determine its general increasing/decreasing trend; and (3) The mean of the

slopes of the HR was used to determine its general increasing/decreasing trend. Figure 1 is

an example of the physiological signals that were derived from two of the forest activity

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temperature is dependent on the overall body temperature. Across day 1 participants,

the average ﬁngertip temperature was 18.8 ◦C, whereas for day 2 and 3 participants, the

average was 30.0 ◦C. In this paper, we will refer to day 1 and the day 1 participants as a “cool

day” and the “cool day participants”, and days 2 and 3 and their respective participants as

“warm days” and the “warm day participants”.

We assessed the effect of the time-of-day based on whether the participants were in the

morning or afternoon group. Day 2 and 3 participants had their associated POMS scores

Int. J. Environ. Res. Public Health 2022, 19, 1231

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taken account in the statistical model (day 1 participants did not have psychological data

collected to be included in this analysis).

2.6.3. Determining the Physiological Effect of Nature Break

To determine if there was a signiﬁcant difference in the physiological signals that

were recorded before and after the Nature Break, a paired samples t-test was used for the

normally distributed physiological features and a Wilcoxon signed-rank test was used for

the non-normally distributed features. A mixed model was used to assess the signiﬁcance

differences across the forest activity segments, with the segment as a ﬁxed effect. A mixed-

model approach was selected in order to take into account the missing data that occurred

due to technical difﬁculties or unclean data.

Control Analysis 1: Ambient Temperature

The participants were divided into cool day (day 1) and warm day (day 2, 3) groups in

order to take into account the signiﬁcant difference in ambient temperatures between these

days. The pre-post analysis and the analysis across the forest activity segments followed the

procedure that was described in Section 2.6.3; morning and afternoon group and pre-forest

POMS scores were not considered in this portion of the analysis.

Control Analysis 2: Time of Day

For both groups, a paired samples t-test or Wilcoxon signed rank test was used to

determine if there was a signiﬁcant difference before and after the Nature Break for each

physiological signal. Independent t-tests were used on the pre-post difference in order

to assess the difference between the morning and afternoon groups. Welch’s t-test was

used when the variances were unequal and a Mann-Whitney U test was used for the

non-normally distributed features. We performed an Analysis of Covariance (ANCOVA)

in order to assess whether the means between the morning and afternoon groups were

signiﬁcantly different post-forest, adjusting for the pre-forest measurements. A mixed

model was used in order to assess the signiﬁcance differences across the forest activity

segments, with segment and time-of-day as ﬁxed effects. For the day 2 and 3 participants

analysis, the ANCOVA also adjusted for pre-forest positive and negative POMS scores and

the mixed model accounted for the pre-forest rounded positive and negative POMS scores.

The p-values from the multiple comparisons between morning and afternoon groups

at each forest activity segment, as well as multiple comparisons between the segments,

were adjusted using the Bonferroni method.

3. Results

3.1. Forest Bathing Increases Positive Mood States and Decreases Negative Mood States

The average POMS scores for the negative mood states signiﬁcantly decreased follow-

ing the Nature Break (p < 0.01), while the average POMS score for the positive mood state

(V) signiﬁcantly increased following the Nature Break (p < 0.05) (Figure 3).

3.2. Purposeful Engagement with the Forest Induces Different Physiological Response Proﬁles

The FB segments had significant effects on all of the recorded physiological features,

including the mean standard deviation of the EDA slopes (p < 0.001 un-adjusted), mean of the

median skin temperature slopes (p < 0.001 un-adjusted), and mean of the average HR values

(p < 0.001 un-adjusted). Figure 4 shows the mean value with a 95% confidence interval of

these three measures across all of the segments and the Bonferroni adjusted p-values.

nt. J. Environ. Res. Public Health 2022, 19, x

Int. J. Environ. Res. Public Health 2022, 19, 1231

8 of 16

Figure 3. POMS results pre-forest and post-forest. T: tension and anxiety, D: depression and dejection,

FiguAr: ean3g.ePr OanMd Shorsetsiluitlyt,sFp: fraet-igfouree, sCt: aconndfupsoiosnt,-fVo:rveisgto.rT. :Sitgennisﬁicoanntadnifdferaennxceiestayr,eDm:adrkeepdrewsisthion and d

tion*,pA<:0.a0n5gaenrd *a*npd<h0.o0s1t. ility, F: fatigue, C: confusion, V: vigor. Significant differences are ma

with * p < 0.05 and ** p < 0.01.

The participants experienced the largest sympathetic arousal, as manifested by their

3.2.EPDuAr,pdouserfiungl Ethnegaogldemtreenet(wseigtmh etnhte 4F)o, rbeasrteIfnoodtuwceaslkDinifgfe(rseengtmPehnyt s5i)o,loagndicaploRste-sfoproenstse Profil

(segment 8) activity segments, and the lowest sympathetic arousal during the pine tree

refTuhgee sFeBgmseengtm(seengmtsehnta7d).sTighenipfiinceantrteeerfefefucgtse soengmalelnot f(stehgemreencto7r)ddeemdopnhstyrsaiteodlothgeical feat

incllaurdgeinstgditfhfeeremnceeatno tshteabnadraefrodotdweavlkiaintigoanndofthtehpeoEstD-foAresstloacpteivsit(ypse<g0m.0en0t1s (upn<-a0.d01ju),sted), m

of tlhikeelmy deudeiatonthsekivnartioeums psteimrautluatriengslaoctpiveistie(spd<ur0in.0g0t1heulnat-taedr tjwusotseedg)m, eanntds. mean of the ave

HR3v),apliSunkeeisntrt(eepme<pre0efr.ua0gt0ue1re(ushenagd-matdehnejutlas7rt)ge,edasnt).rdaFtpeigoosufti-rnfeocrr4eeasssthe(osdewugrmsinetghnttehe8m)braeecaatntihviivntyaglasuecetgimvwiteyint(htsse,aglmi9k5eenl%yt confid

inteinrdviaclatoinf gthreelsaexatthiorne.e Tmheisafseuartuerseahcardosthseallalrogefstthreatseeogfmdeecnrtesasaenddurtihneg Bthoenbfaerrerfoonoti adjust

valwuealsk.ing activity (segment 3), likely reﬂecting focus and attention. The barefoot walking

activity demonstrated a signiﬁcantly lower skin temperature slope than all of the other

segments, with a signiﬁcance of p < 0.001. The post-forest activity segment (segment 8)

was also signiﬁcantly different from all of the other segments, with p < 0.01; except for the

breathing (segment 3) and pine-tree refuge (segment 7) segments.

Heart rate was highest during the breathing activity and lowest during the post forest

activity segment. The breathing activity induced a signiﬁcantly higher heart rate compared

to all of the other segments (p < 0.001) and, following this activity, there was a downward

trend of the mean HR. The mean of the median HR slopes showed no signiﬁcant differences

across the segments.

3.3. Ambient Temperature Has an Effect on Skin Temperature and Heart Rate Response

For the cool day’s participants, the average standard deviation of the EDA slopes

and median of the skin temperature slopes were signiﬁcantly higher following the Nature

Break (p ≤ 0.001, p < 0.05). For the warm days’ participants, the mean average HR was

signiﬁcantly lower and the average median of the skin temperature slopes was signiﬁcantly

higher following the Nature Break (p = 0.001, p < 0.05).

InItn. tJ.. JE. nEvnivroirno.nR. Rese.sP. PuublbilcicHHeaealtlhth22002222, ,1199, ,1x231

9 o9fof1716

Figure 4. Effect of forest bathing on the mean standard deviation of the EDA slopes, mean of the

mFeigduiarne t4e.mEpffeercattuofrefosrloepstesb,aathnidnmg eoanntahveemraegaenhsetaarntdraatredadcerovsiastaiollnfoorfestht eacEtiDviAtyssloegpmese,nmtse.a*npo<f 0th.0e5,

**mpe<di0a.n01t,em***pper<at0u.r0e01s,loBpoensf,earnrodnmi aedajnusatveedrapg-veahlueeasr.t rate across all forest activity segments. * p <

0.05, ** p < 0.01, *** p < 0.001, Bonferroni adjusted p-values.

Across the forest activity segments, participants from both the cool and warm days

exhibiTtehde spiagrntiicﬁicpaannttds iefxfepreerniecenscefodrtahlel olafrtgheestpshyymsipoalothgeictaicl aferaotuusraels,.aTshmeamniefaenstaedvebryagteheHirR

wEaDsAth, eduhriignhgetshtedoulrdintgreteh(esebgrmeaetnhtin4g), abcatrievfiotyot(wseaglmkinengt(3se)gamndendte5m), oannsdtrpaotestd-faorgeesnt (esreagll-y

dmecerneta8s)inagctitvreitnydsefgomlloewntisn, gantdhitsheselgowmeesnttsfyomr pbaotthhettihcearcoouoslaal nddurwinagrtmhedpainyeptarereticreipfuagnets.

Tsheigsmseegnmt (esengtmweansts7ig).nTiﬁhceapnitnlye tdriefeferreefnutgferosemgmalelnotf(tsheegmotehnetr7s)edgemmeonntsstfroartetdhethceoolalrdgaeyst’s

pdairftfiecriepnacnetstoantdhealblaorfetfhooetowthaelrksineggmanendtsth, eexpcoepstt-ffoorretshteapctriev-iftoyressetgamcteinvtitsy(pse<gm0.0en1)t,, lfiokretlhye

wdauremtodtahyes’vparairotuicsipsatinmtsu.lating activities during the latter two segments.

Int. J. Environ. Res. Public Health 2022, 19, 1231

10 of 16

The barefoot walking section (segment 5) induced the largest decrease in heart rate

for the cool day’s participants and was signiﬁcantly different from the sitting on stumps

segment (segment 2) and the post-forest activity segment (segment 8) (p < 0.05); the latter

two segments demonstrated the largest increase in heart rate. In contrast, the barefoot

walking segment induced the largest increase in heart rate for the warm days’ participants

and was signiﬁcantly different from all of the other segments, apart from the post-forest

activity segment (p < 0.05).

The cool day’s participants experienced a decrease in skin temperature during the

pre-forest and post-forest activity segments (segments 1 and 8), whereas the warm days’

participants experienced the largest increase in skin temperature during these segments.

Participants from all of the days experienced the largest or second largest decrease in

skin temperature during the barefoot walking segment (segment 5). This segment was

signiﬁcantly different from all of the other segments for the warm days’ participants

(p < 0.001), and all of the other segments, except the pre-forest, old tree, and post-forest

activity segments (segments 1, 4, and 8), for the cool day’s participants (p < 0.05). These

differences are consistent with the expected effects due to the diverging vasoconstriction

and vasodilation response on hot and cold days, respectively.

3.4. Circadian Rhythms Affect Skin Temperature Response to Forest Bathing

The participants from all of the days demonstrated a significant difference between

morning and afternoon groups for the change in average median of the skin temperature

slopes pre-forest to post-forest (segment 1 to 8) (p ≤ 0.001). The afternoon had a smaller

change in skin temperature slopes post-forest from pre-forest than the morning group. Cool

day participants also saw a smaller difference in average heart rate post-forest from pre-forest

in the afternoon group (p < 0.05). No other features demonstrated a significant difference

between morning and afternoon groups in terms of pre-forest to post-forest differences.

Results of the ANCOVA showed no signiﬁcant effect of time-of-day for the cool day’s

participants, meaning there was no signiﬁcant difference between morning and afternoon

group post-forest when adjusted for the pre-forest measurements. For the warm days’

participants, the average median of the skin temperature slopes showed a signiﬁcant effect

of time-of-day (p = 0.001). The afternoon group experienced less of an increase in skin

temperature post-forest than the morning group, with a signiﬁcance of p = 0.001. The other

features for the warm days’ participants showed no signiﬁcant difference between morning

and afternoon groups at the post-forest activity segment when adjusted for pre-forest

measurements, pre-forest POMS scores, and time-of-day.

3.5. Participants Have Signiﬁcant Physiological Differences Pre- and Post-Forest Bathing

To facilitate the comparison of the results from this study to those of previous research,

we also conducted a physiological analysis pre- and post-forest bathing. Across the par-

ticipants, the average of the standard deviation of the EDA slopes and the median skin

temperature slopes were signiﬁcantly higher after the forest (p < 0.05, p < 0.01) and the

average heart rate was signiﬁcantly lower after the forest (p < 0.01) (Figure 5).

Notably, the post-forest physiological data included a segment where participants

engaged in a discussion about their forest experience, in which several participants were

visibly emotional. This may have confounded the post-forest physiological signals, result-

ing in the “post” segment not being representative of “post” intervention, but of a ﬁnal

active ingredient of the FB experience.

3.5. Participants Have Significant Physiological Differences Pre- and Post-Forest Bathing

To facilitate the comparison of the results from this study to those of previous re-

search, we also conducted a physiological analysis pre- and post-forest bathing. Across

the participants, the average of the standard deviation of the EDA slopes and the median

Int. J. Environ. Res. Public Health 2022, 19, 1231skin temperature slopes were significantly higher after the forest (p < 0.05, p11<o0f .1061) and

the average heart rate was significantly lower after the forest (p < 0.01) (Figure 5).

Figure 5. Effect of foFriegsut rbeat5h. inEgffoenct tohfe fmoreeasnt bstaatnhdinagrdodnetvhieatmioneaonf stthaenEdDarAd sdleovpieast,iomneoanf tohfethEeDmAesdloiapneste, mmpeearnatoufre

slopes, and mean avethraegme hedeaiarnt rtaetme fpreormatupre-sfolorpesetsa, catnivditmy eseagnmaevnetratogephoseta-rftoreastteafcrtoimvitpyrsee-gfomresntt.a*ctpiv<it0y.0s5e,g*m* pen<t0t.o01,

paired t-test and Wilpcoxsto-nfosriegsnt eadctrivaintky tseesgtm. ent. * p < 0.05, ** p < 0.01, paired t-test and Wilcoxon signed rank test.

4. DiscussiNonotably, the post-forest physiological data included a segment where participants

Thenegaaigmedoifnthaids istcuudssyiownaasbotoutetxhpeliorrfeortheset efxfpecetrsieonfcea,nininwtehriacchtisveev,egraulidpeadrtinciaptaunrets were

activitvyisoinblpyheymsiootliogniacla. lTahnisdmpasychhaovleogcoicnafloruenspdoednstehse. pPossytc-fhoorleosgtipchalylysi,otlhoegpicaarltsicigipnanlst,sresult-

showeidnga isnigtnhieﬁ“capnotstd”escergeamsenitnntohteibrenineggarteipvreeaseffnetcattiavnedoaf “spigonsitﬁ”cianntet rivnecnretiaosne,ibnutthoefira final

positivaecatifvfeecitnfgorlleodwieingt oafNthaetuFrBe eBxrpeaekri.eTnhce.physiological responses changed signiﬁcantly

according to the different activities within the forest, with participants also experiencing

signiﬁc4a. nDtipshcuyssioiolongical differences before and after the Nature Break. Our results suggest

that interacTtihvee aniamtuoref athctisivsittuiedsyhawvaesptooseitxivpelopresytchheoeloffgeicctaslobfeanneﬁitnstearnadctdiveem, ognusidtreadtentahteure ac-

feasibitliivtyityofounsinpghywsieoalroagbilcealseannsdorps styocmhoolnoigtoicrapl hreysspioolnosgeisc.alPrseyscphoonlosegsicianllay,nathtueraplaisrttiiccipants

forest bshaothwinegd aactsiivgintyi.ficant decrease in their negative affect and a significant increase in their

ApgorsoitwiviengafbfeocdtyfoolfloewviidnegncaeNshaotuwres tBhraetaFkB. Tahnedpnhaytusiroelowgaiclkasl rpersopvoidnseeqsucahnatniﬁgaebdlesignifi-

physiocloangitclyalaacncdormdeinngtatlobtehneeﬁdtisffteorehnutmaacntivbietiinesgsw, situhcihnatshreefdourecisnt,gwcoitrhtispoalrlteicvieplas,nHtsRa,lasnodexperi-

nblaotoudreepanrcectisinsvguitrsyeigi[nn3,ci5fri,ec1aa2sn,1ets4p,p4h8oy,s4sii9toi]vl.oeTghmicisaolosdtduifdsfteyartepenrsoc, evdsiedbceersefoafruseerstahnnedergaeafvttieidvreetnhmceeoNtohadtautsrtaeantBeirsne,taaekrn.adOcthuivaresresults

signiﬁcant effects on physiological state. We found signiﬁcant responses across all of the

four physiological ANS features during the various activities of the Nature Break, indicating

the potential for using a wearable sensor to monitor the effects of deliberate engagement

with nature.

Previous studies using the POMS questionnaire found that negative mood states im-

proved and positive mood states increased following a forest bathing and nature walk activ-

ity [4,8,11,49]. Other studies that have looked at purposeful engagement with nature have

also reported mood enhancement and overall satisfaction with the nature session [29–31].

Our ﬁndings support this trend as well, providing further evidence that an interactive,

guided nature activity can provide positive psychological experiences to humans. Cox,

Shanahan, et al. (2017) deconstructed the nature experiences of 1023 residents of an urban

population in the UK and found that a person’s connection to nature was positively corre-

lated with them spending time in nature [50,51]. By fostering a positive forest experience,

we anticipate that the Nature Break will similarly lead to participants spending more time

in a forest environment in the future.

Few studies have assessed the effect of forest bathing in-situ using wearable sen-

sors [25,49]. We showed that different activities conducted within the forest environment

have different physiological effects, which contribute to creating a dynamic, embodied

experience of immersion in nature. The participants across all of the days showed, in

general, a decreasing average heart rate across the forest activity segments. These results

are consistent with previous studies that have measured the effects of exposure to nature

Int. J. Environ. Res. Public Health 2022, 19, 1231

12 of 16

on heart rate [19,25,34,49,52,53]. EDA and peripheral skin temperature have received little

attention in the context of FB and nature walks and studies that have investigated EDA

did not report any signiﬁcant ﬁndings [25,27]. Reeves et al. (2019) and Chen et al. (2018)

have used EDA to assess ANS activity, speciﬁcally as a measure of physiological stress and

arousal. Reeves et al. (2019) found no signiﬁcant effects of site (wetland, control, urban)

on tonic or phasic EDA. Chen et al. (2018) did not report speciﬁcally on EDA alone, but

combined it with ECG measures to predict arousal and used HR and facial EMG to predict

the valence. Chen et al. (2018) also measured skin temperature in their study, however

they did not mention how it was used to contribute to their assessment of ANS activity. In

contrast, we saw signiﬁcantly greater standard deviation of the EDA slopes—indicating

larger numbers of electrodermal reactions—and median of the skin temperature slopes

post-forest compared to pre-forest across all participants.

Across the forest activity segments, the participants from all of the days had the largest

sympathetic activity during the post-forest discussion (segment 8), old tree (segment 4),

and barefoot walking (segment 5) segments, as manifested by their EDA, likely due to the

various activities of touching, smelling, walking on dirt, and emotional discussion during

these segments. As well, a lower standard deviation of the EDA slopes was observed

during the pine tree refuge segment (segment 7), likely reﬂecting relaxation [38]. Peripheral

skin temperature saw the greatest rate of decrease during the barefoot walking segment

(segment 5) across all participants, likely reﬂecting the mental stimulation associated with

focusing on the barefoot walking task [38]. Higher rates of increase in the peripheral skin

temperature typically reﬂect mental relaxation and these were seen during segments such

as the deep breathing, pine tree refuge, and post-forest activity segments (segments 3, 7,

and 8) [38,43].

We found that the ambient temperature mainly had an effect on the skin temperature

and heart rate response. The largest rate of decrease in the heart rate occurred during the

barefoot walking segment (segment 5) for the cool day’s participants, however the warm

days’ participants experienced the largest rate of increase during this segment. Similarly,

the cool day’s participants showed a decrease in skin temperature during the pre-forest

and post-forest section (segment 1 and 8), but the warm days’ participants had the largest

increase in skin temperature during these segments. Differences in the rate of skin tempera-

ture change during the pre-forest and post-forest activity segments may be attributed to

the difference in the ambient temperatures of those days and the presence of direct sunlight

or overcast weather. The ambient temperature and other meteorological elements may also

affect the ground temperature, which could have an impact on HR response during the

barefoot walking segment [54]. In their study, Korhonen (2006) examined HR response

in men who were exposed to local cold exposure and whole-body cold exposure. They

found that local cold exposure to the feet increased the HR, while consistent whole-body

exposure to cold lowered the HR [55]. Similar effects may characterize the difference in the

HR responses in the cool day’s and warm days’ participants due to the variances in the air

and surface ground temperatures.

Circadian rhythms also affected skin temperature. The skin temperature in the af-

ternoon groups had a smaller change from pre-forest to post-forest. For the warm days’

participants, the afternoon groups’ skin temperatures increased less than the morning

groups’ at the post-forest activity segment. The limited amount of meteorological data

from this area limits our ability to explain this result as an effect of the changing ambient

temperature throughout the day.

The results of this study need to be considered in light of several limitations. First,

Venables and Mitchell (1996) suggest the importance of considering the interaction between

the time of the day and the season with sex, as females may be more responsive to these con-

ditions than men [56]. In addition to possible differences in physiological response between

the genders, different physical environments may also induce varying psychological re-

sponses. Park et al. (2011) studied the relationship between various physical environments

in forests and psychological responses; they found that they were signiﬁcantly related [57].

Int. J. Environ. Res. Public Health 2022, 19, 1231

13 of 16

This study did not account for the differences between the genders, nor other physical

factors, apart from the average air temperature. Second, the participants were not required

to perform the various exercises in the Nature Break. For example, some participants did

not take off their shoes and socks to do the barefoot walking segment, which may have

confounded the current results. Third, the wearable sensor would occasionally disconnect

from the mobile application due to a Bluetooth malfunction. These intermittent disconnec-

tions accounted for several participants’ data being missing or too short to contribute to

the analysis. Furthermore, when these moments occurred, a researcher had to intervene

to check the equipment; this may have disrupted the complete immersive experience of

the Nature Break activity. Fourth, there may be an effect of physical activity on the phys-

iological responses in addition to the response from the forest bathing experience itself.

Olafsdottir et al. (2020) investigated the effects of leisure walking in a natural environment

against passive exposure to nature and physical exercise alone. They found that walking in

nature improved mood more than just watching nature or doing physical exercise alone.

They also found that, during a more stressful time period, walking in nature lowered

cortisol levels more than nature viewing [48]. Hansen et al. (2017) also mentioned that

multiple studies limited physical activities for each activity to 20 min in order to control for

the effect of physical exercise on cardiovascular measures [3]. Although in this study we

did not disentangle the effects of exercise on the physiological response from the effects

of forest bathing, results from previous studies indicate that the act of walking may have

contributed to the positive effects reported in our study.

Our study has shown that it is possible to use wearable sensors in order to monitor

forest bathing experiences and this has signiﬁcant implications for all organizations that

aim to quantify the effect of nature on human physiology. Our results support using

technology for a more evidence-based approach to forest bathing. They set the stage for

future work that uses the distinct physiological response proﬁles that are associated with

speciﬁc forest activities as a scaffold to guide the design of a forest immersion experience

according to the intended outcome. Future work can also build upon the feasibility of using

wearable sensors for moment-by-moment physiological monitoring in the forest to detect

signiﬁcant moments and activities for speciﬁc participants in real-time, allowing guides to

tailor and customize the forest experience to the individual forest bather.

5. Conclusions

We found that an interactive, guided nature activity increases positive mood states

and decreases negative mood states. The various exercises in the forest had signiﬁcant and

varying physiological effects. In general, during the forest activity segments that involved

more external stimuli that required focus and attention, such as walking barefoot in the

forest or discussing personal experiences in the forest, the participants experienced a larger

sympathetic activation; whereas, during the segments of introspection and relaxation, the

participants experienced a larger parasympathetic activation. We found that there were

differences in the physiological responses due to circadian rhythm, however we are not

able to consistently report a main ﬁnding. For future forest bathing initiatives, we highlight

the possibility of creating a program that is shaped by a target physiological response.

Author Contributions: Conceptualization, E.T.M., H.M., S.B.-M.; methodology, E.T.M., H.M. and

S.B.-M.; data collection, D.F., N.I.S. and S.B.-M.; formal analysis, D.F. and S.B.-M.; writing—original

draft preparation, D.F.; writing—review and editing, D.F., N.I.S., S.B.-M.; supervision, S.B.-M.; project

administration, N.I.S., S.B.-M.; funding acquisition, S.B.-M. All authors have read and agreed to the

published version of the manuscript.

Funding: This study was funded by the Natural Sciences and Engineering Research Council (NSERC)

of Canada [Discovery Grant RGPIN-2016-03817; Engage Plus EGP2544529-19].

Institutional Review Board Statement: This study was approved by the Institutional Review Board

of McGill University (study number A10-M53-19A).

Int. J. Environ. Res. Public Health 2022, 19, 1231

14 of 16

Informed Consent Statement: Informed consent was obtained from all of the subjects who were

involved in the study.

Data Availability Statement: The physiological and POMS data that were used to support the

ﬁndings of this study are available from the corresponding author upon request.

Acknowledgments: The authors would like to thank R.M Ochoa, N. Kuhlmann for helping with

the data collection, J. Correa for his help with the statistical analysis, and M. Bouchard for his

technical support.

Conﬂicts of Interest: The authors declare no conﬂict of interest. The funders had no role in the design

of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or

in the decision to publish the results.

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