Available online at:
https://cc.arcabc.ca/islandora/object/cc%3Apsycjournal

J Camosun Psyc Res. (2021). Vol. 3(2), pp. 72-85.
Submitted Winter 2021; accepted July 2021.

What Biological Mechanisms Involved with Physical
Activity Determine the Reduction of Stress and Anxiety?
Authors: Emma Rennie* and Abby Rothwell
Supervising Instructor: Michael Pollock, Psyc 215 (“Biological Psychology”)
Department of Psychology, Camosun College, 3100 Foul Bay Road, Victoria, BC, Canada V8P 5J2
*Corresponding author email: emma_rennie@icloud.com

ABSTRACT
In this research paper, we aim to gain a better understanding of the biological functions that
occur when an individual takes part in physical activity, especially in regard to their stress and
anxiety levels. Previous research has shown that physical activity can increase serotonin levels,
decrease amygdala activity, and increase irisin levels. We measured physical activity by minutes
of exercise, rated serotonin levels through number of minutes slept, determined amygdala
activity from heart rate after viewing scary stimuli, and inferred irisin levels after measuring
Body Mass Index (BMI) each day. Our correlational study results showed that the serotonin
levels, amygdala activity, and irisin levels were not significantly correlated with physical activity
levels.
1. Introduction

as well as how to use exercise as a method
of stress and anxiety reduction.

1.1 Research Problem
1.2 Literature Review
Physical exercise is an option for people
to reduce their stress and anxiety.
Understanding what biological mechanisms
are involved in that process can help
individuals create better balance between
their physical and mental health. With more
knowledge, physical activity can be used
more efficiently as a tool for lessening
anxious feelings. This information will
provide individuals new ways to cope with
their anxiety and stress disorders while also
promoting healthier alternatives to
prescribed medications. We would like to
find out what causes physical activity to
reduce stress and anxiety levels. With the
findings, we can teach others the importance
of exercise for physical and mental health,

One factor that has been found that
significantly increases serotonin levels in the
brain is any form of physical activity. A
great deal of research conducted in this field
of study is done using either physiological
or neuropsychology methods. The reason
why physiological psychology is so popular
in regards to research about cognitive
performance and anxiety levels is due to the
fact that experimenters can use lab rats to
observe the neural mechanisms under
conditions that may be unethical to do with
human participants. In a study conducted
last year in Beijing, researchers explored the
biological benefits that treadmill exercise
has on disorders such as Posttraumatic
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Stress Disorder (PTSD). The experiment
was demonstrated on a time-dependent
sensitization model which mimics certain
disorders such as PTSD (Zhang et al, 2020).
This model was developed to evaluate the
possible PTSD-like symptoms after
moderate treadmill exercise in a 4-week
running program. In the experiment, 47 rats
were randomly assigned into four separate
groups and were subjected to various
elements such as restrainment and electric
shocks to their body; causing the rats to
develop fear conditioning (Zhang et al,
2020). Certain groups of rats were
administered an antidepressant, Sertraline,
which affects chemicals in the brain that
may be unbalanced due to anxiety or
depression. To determine the levels of
monoamine neurotransmitters in the rats, the
researchers injected high performance liquid
chromatography technology that would
allow them to observe the neurotransmitters
at work (Zhang et al, 2020). The results
concluded that the DA levels in the
prefrontal cortex that is attributed to anxiety
decreased in the rats that were exposed to an
intense stressor, such as electric shock, after
moderate treadmill exercise (Zhang et al,
2020). It was reported that the treadmill
exercise significantly increased serotonin
levels in the hippocampus as well as
decreased dopamine levels in the prefrontal
cortex (Zhang et al, 2020). These results
supported the researchers hypothesis in that
treadmill exercise reduces fear conditioning
and anxiety-like behaviour due to biological
mechanisms such as an increased 5-HT level
in the hippocampus and decreased DA levels
in the prefrontal cortex (Zhang et al, 2020).
Consistent exercise can contribute to
anxiety reduction from reactivity in the
amygdala. Chen et al. (2019) have looked at
how regular exercise alters activity in the
amygdala when a person perceives a happy
or fearful face in an implicit or explicit

expression after physical activity. Chen et al.
(2019) used implicitly and explicitly
expressed emotions to test levels of
perceptions based on how well a person can
identify the emotion of happy or fearful.
Implicit expression would be someone not
outwardly expressing an emotion on their
face, where explicitly would be an
expression outwardly showing on their face
so a person could easily identify the
emotion. In the implicit condition Chen et al.
(2019) used a medical face mask to cover
the noise and mouth of the face being shown
to the participant. The experiment used forty
human volunteers (Chen et al., 2019).
Subjects completed a survey on habitual
physical activity and a survey on anxiety
traits at the start of the experiment (Chen et
al., 2019). There was a running and a
walking condition which consisted of a 3minute warm up, 12 minutes walking or
running, and a 10-minute cool down (Chen
et al., 2019). After the running or walking
session was done the subject filled out a
survey on the state of their anxiety (Chen et
al., 2019). Next the subject had a 20-minute
fMRI scanning session (Chen et al., 2019).
The stimuli used for the fMRI scanning were
black and white photos with male and
female faces in the expression of either
happy, fearful, or neutral with the faces
coloured red, yellow, or blue (Chen et al.,
2019). The fearful and happy emotions were
explicitly expressed and implicitly expressed
(Chen et al., 2019). Fearful and happy faces
that were explicitly expressed where faces
that had non-masked faces and the emotions
that were implicitly expressed had face
masks on the persons with happiness or
fearfulness (Chen et al., 2019). Subjects
were shown a randomly selected face for
200-ms and then allowed 1200-ms to
identify the colour of the face shown (Chen
et al., 2019). After the fMRI scanning
subjects were shown the faces again and
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were told about the three emotional states of
the faces that were either explicitly
expressed or implicitly expressed (Chen et
al., 2019). Then the subjects had to go
through the same process as the fMRI but
identifying the emotional state of the face
presented (Chen et al., 2019). Chen et al.
(2019) analysed the amygdala and looked at
the relationships between habitual physical
activity, anxiety lowering effect from acute
exercise and physical fitness. During the
explicitly expressed fear condition, the
walking had more activity in the amygdala
compared to the running and during the
explicitly expressed happiness condition
running had less activity in the amygdala
(Chen et al., 2019). In the running, there was
a stronger reactivity in the amygdala in
regard to the implicit happiness condition
compared to the fear and the walking had
stronger amygdala reactivity to implicit fear
(Chen et al., 2019). There was a positive
correlation with consistent exercise resulting
in anxiety reduction and reactivity in the
amygdala (Chen et al., 2019). There is less
activity in the amygdala after a short amount
of exercise which contributes to feelings of
anxiety reduction after physical activity.
Anxiety could be reduced by the amount
of irisin in the body after consistent exercise.
There is a correlation between anxiety
reduction, voluntary exercise and increased
levels of irisin in the brain as well as in
white adipose tissue (Uysal et al., 2018).
Uysal et al. (2018) conducted an experiment
with two groups of mines, one control group
and one exercise group. For 6 weeks, the
exercise group had access to a running
wheel and the control group did not (Uysal
et al., 2018). After the 6 weeks the two
groups were put through an “open field
test”, where each mouse was put in a 1 X 1
m area for 5 minutes and measured
locomotor activity and anxiety (Uysal et al.,
2018). Uysal et al. (2018) then used a

“elevated plus maze test” to observe anxiety
in the mice. The maze consists of a middle
platform with 4 arms connected to the
middle, two open and two closed arms
(Uysal et al., 2018). The mice were observed
for 5 minutes, measuring the time on both
the open or closed arms (Uysal et al., 2018).
The last component of the experiment was
analyzing blood and tissue samples from the
mice in the controlled and exercise group as
well as weighting the irisin levels (Uysal et
al., 2018). The results of the “open field
test” showed that the exercise group had
increased movement and speed and stayed to
the centre of the field compared to the
control group (Uysal et al., 2018). In the
“elevated plus maze test” the mice that were
a part of the exercise group spent more time
in the open arms than the mice in the control
group (Uysal et al., 2018). Uysal et al.
(2018) discovered that in the mice of the
exercise group had higher levels of irisin in
the brain, brown adipose tissue, white
adipose tissue, kidney, and the pancreas.
There was a positive correlation between
irisin levels in the brain and irisin levels of
white adipose tissue and with activity in the
“open field test” and the “elevated plus maze
test” (Uysal et al., 2018). Another
correlation was found in irisin levels of
brown and white adipose tissue as well as
irisin levels in kidneys were correlated with
adipose tissue (Uysal et al., 2018). These
results can help us understand that voluntary
physical activity can lead to higher levels of
irisin (Uysal et al., 2018).
1.3 Hypotheses
Based on the above literature review, we
predicted the following hypotheses:
 Hypothesis #1: If the amount of physical
activity increases, then the serotonin will
increase.
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



Hypothesis #2: If the amount of physical
activity increases, then the amygdala
activity will decrease.
Hypothesis #3: If the amount of physical
activity increases, then the irisin levels in
the body will increase.

2. Methods
2.1 Participants
The two authors of this paper were also
the participants in its studies. The
participants were both female, aged 22 and
27. Both participants were undergraduate
students at Camosun College enrolled in
Psychology 215- Biological Psychology.
The participants shared a common interest in
physical activity and regularly engaged in
some form of exercise.
2.2 Materials and Procedure
We conducted a correlational study to test
all three of our hypotheses by examining the
levels of the variables in a normal day. Each
participant kept a notebook with them
during the study’s two week period, which
was how they recorded their selfobservations. The three variables that were
being measured were: (1) physical activity
(2) serotonin level, (3) amygdala level and
(4) irisin level.
To measure the amount of physical
activity each participant recorded the
number of minutes of exercise. The minutes
were logged in the participants notebook on
the days of physical activity. Physical
activity was defined as medium to high
intensity which included biking, yoga, and
weight lifting.
To measure the level of serotonin
released, each participant recorded in their
notebook how many minutes of sleep they

got. The amount of sleep was when the
participant fell asleep till when they woke up
in the morning. These observations were
recorded first thing in the morning after
waking up on days where they had no
physical activity as well as on days of
physical activeness.
To measure the levels of response in the
amygdala, each participant measured their
heart rate changes in response to a scary
stimulus. The scary stimuli consisted of 30second videos found on Youtube that were
different daily. The participants recorded in
their notebook their heart rate before they
were shown the video and directly after they
were shown it. These observations were
recorded on days where there was no
physical activity as well as on days where
they were physically active. In order to
measure heart rate before and after being
shown the scary stimulus, the participants
placed two fingers against their wrist and
counted the beats for 15 seconds. They then
multiplied the numbers of beats by 4 to find
out their heart rate per minute.
To measure the level of irisin, the Body
Mass Index (BMI) was used. Each
participant weighed themselves on a scale
each day for two weeks. The participants
logged their weight in their notebook and
then did the BMI calculation. Weight in
kilograms divided by height in meters
squared equals BMI. The formula is BMI =
kg/m2.
To assess the strength and statistical
significance of associations between
variables predicted by our three hypotheses,
we performed Pearson product moment
correlations of their predictor variables
(serotonin level, amygdala response and
irisin level) with their outcomes variable
(anxiety levels). For testing Hypothesis #1,
we correlated the high level of serotonin
released in the participant with their amount
of physical activity. For Hypothesis #2, we
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correlated the decrease in amygdala
activation with the participants amount of
physical activity. For testing Hypothesis #3,
we correlated the high level of irisin released
in the participants body with their amount of
physical activity. We performed all of the
above correlations separately for each
participant as well as using data pooled
across all of the participants. For the
correlations using pooled data, in addition to
using the raw data, we also performed
correlations after we had first transformed
the data from each participant into z-scores
in order to standardize differences in
averages and variability seen between the
participants in their data and thus make them
more comparable. A correlation coefficient
was considered statistically significant if the
probability of its random occurrence (p) was
<.05 (i.e., less than 5% of the time expected
by chance alone).
3. Results
As shown in Table 1, all three variables
were not significantly correlated with
reduced anxiety levels. For the outcome
variable for serotonin, tested through
minutes of sleep, the results from the pooled
standardized data were not significant (r =
.03, p = .86; see Figure 1B). The pool raw
data for serotonin was also not significant (r
= .22, p = .259; see Figure 1A). Irisin levels
and minutes of exercise were not significant
in the results from the pooled standardized
data (r = .33, p = .085; see Figure 3B);
furthermore, the pooled raw data shows it
was significant (r = .54, p = .00248; see
Figure 3A). Lastly, the results from the
amygdala and heart rate per minute were not
significant from the pooled standardized
data (r = .09, p = .66; see Figure 2B);
however, the pooled raw data shows it was
significant (r = .42, p = .02; see Figure 2A).

4. Discussion
4.1 Summary of Results
Based on previous research, we
hypothesized that three different variables
would decrease anxiety levels after physical
activity: the serotonin level (Hypothesis #1),
the irisin level (Hypothesis #2), and the
amygdala activity (Hypothesis #3). Data
pooled across participants in our correlation
study did not support any of our hypotheses
in the relationship between amount of
exercise with serotonin levels, irisin levels,
and amygdala activity (Hypotheses #1, 2, &
3).
4.2 Relation of Results to Past Research
Our correlation study between two
variables, physical activity and serotonin
levels, did not produce statistically
significant results. Our prediction was based
on previous research involving lab rats by
Zhang et al. (2020). These researchers had
found that treadmill exercise produced
biological benefits for disorders such as
Posttraumatic Stress Disorder (PTSD).
Zhang et al. (2020) reported that the
physical activity significantly increased
serotonin levels in the hippocampus, as well
as decreased dopamine levels in the
prefrontal cortex; therefore, their research
demonstrated that exercise can reduce
anxiety-like behaviour. For our study, we
measured serotonin levels by recording how
many minutes of sleep per night the
participants got, as well as recorded their
amount of physical activity during the day.
Contrary to our hypothesis, our participants
did not consistently experience an increase
in serotonin on days in which they engaged
in physical activity. This could be due to
environmental factors that could have
affected their sleep, as well as lifestyle
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variability. In Zhang et al. (2020) study,
their lab rats were in a controlled
environment to reduce any potential
conflicting variables. This controlled
environment could have produced more
accurate results compared to our research
model. Another difference between our
research and the previous research
conducted is that Zhang et al. (2020)
injected high performance liquid
chromatography technology into their lab
rats as a way to observe their
neurotransmitters. In our study, we did not
administer any chemicals or liquid
chromatography technology into our
participants. Future studies in this area
should examine if getting the recommended
amount of sleep per night increases humans
serotonin levels.
Our correlation study between physical
activity and amygdala activity failed to
represent a relationship. This prediction was
made after previous research. Chen et al.
(2019) had found that after a participant did
physical activity and then was exposed to
scary stimuli, their amygdala would
decrease in activity. In contrast, our
participants did not consistently experience a
decrease in amygdala activity to scary
stimuli on days with more minutes of
exercise. This could be due to the way in
which the amygdala activity was measured
as well as the timing of the measuring after
physical activity. The way Chen et al. (2019)
measured amygdala activity in their
participants was using a fMRI scanning.
This could produce more accurate results
compared to our method of using heart beats
per minute. Another aspect that differed
between Chen et al. (2019) and our study
was the timing in between physical activity
and the measuring of amygdala activity after
scary stimuli. In Chen et al. (2019) lab they
gave the participants a ten minute cool down
and then participants filled out a survey,

then continued onto the fMRI scan. In our
study there was varying amounts of time in
between the physical activity and the
measure of amygdala activity using heart
rate per minute. Future studies should
examine whether amygdala activity is able
to predict that physical activity reduces
anxiety.
In our correlation study we could not
confirm a relationship between irisin levels
and physical activity. Uysal et al. (2018) had
discovered that through voluntary exercise
there could be higher levels of irisin found
within the body. Our participants did not
always find an increase in irisin levels after
days with more minutes of exercise. Uysal et
al. (2018) had done this study on mice
compared to us who performed the
correlation study on ourselves. This aspect
could be a large component as to why we
failed to find a correlation. Uysal et al.
(2018) were able to dissect the mice after the
experiment to weight the amount of irisin.
We did not have access to this method so we
had to use Body Mass Index (BMI) to
measure irisin levels in us. The results that
we got were most likely less accurate to the
different methods of measuring irisin. Future
studies should examine whether irisin levels
are able to be predicted in humans instead of
mice after physical activity.

References
Chen, Y.-C., Chen, C., Martínez, R. M.,
Etnier, J. L., & Cheng, Y. (2019).
Habitual physical activity mediates the
acute exercise-induced modulation of
anxiety-related amygdala functional
connectivity. Scientific Reports, 9(1),
19787. https://doiorg.libsecure.camosun.bc.ca:2443/10.103
8/s41598-019-56226-z
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Uysal, N., Yuksel, O., Kizildag, S., Yuce,
Z., Gumus, H., Karakilic, A., Guvendi,
G., Koc, B., Kandis, S., & Ates, M.
(2018). Regular aerobic exercise
correlates with reduced anxiety and
increased levels of irisin in the brain and
white adipose tissue. Neuroscience
Letters, 676, 92–97. https://doiorg.libsecure.camosun.bc.ca:2443/10.101
6/j.neulet.2018.04.023

Zhang, J., Xue, R., Li, Y.F., Zhang, Y., &
Hong-Wen WEI. (2020). Anxiolytic-like
effects of treadmill exercise on an animal
model of post-traumatic stress disorder
and its mechanism. Journal of Sports
Medicine & Physical Fitness, 60(1), 172–
179. https://doiorg.libsecure.camosun.bc.ca:2443/10.237
36/S0022-4707.20.10120-8

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Table 1
Correlation coefficient (r) values, with number of daily trials (n) per correlation in brackets.

Variables
correlated

Participant
#1

Participant
#2

Pooled
raw data

Pooled
standardized
data

Serotonin Level &
Physical Activity

-.25(14)

.18(14)

-.22(28)

-.03(28)

Amygdala Activity
& Physical Activity

-.17(14)

0.00(14)

.42(28)*

-.09(28)

Irisin Level &
Physical Activity

-.14(14)

-.52(14)

-.54(28)*

-.33(28)

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Figure 1
Scatterplot of Physical Activity and Serotonin Level using pooled (A) raw and (B) standardized
data across participants.
A

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B.

Marker color indicates which participant data is from: red = participant #1, orange = participant
#2. Some data might not be visible in the figure due to overlapping markers.

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Figure 2
Scatterplot of Physical Activity and Amygdala Activity using pooled (A) raw and (B)
standardized data across participants.
A.

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B.

Marker color indicates which participant data is from: red = participant #1, orange = participant
#2. Some data might not be visible in the figure due to overlapping markers.

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Figure 3
Scatterplot of Physical Activity and Irisin Level using pooled (A) raw and (B) standardized data
across participants.
A.

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B.

Marker color indicates which participant data is from: red = participant #1, orange = participant
#2. Some data might not be visible in the figure due to overlapping markers.

85