The the relationship between the intensity of exercise

            The benefits of exercise and physical activity on the
human body are countless, ranging anywhere from building and strengthening
muscles (e.g. cardiac), to preventing diseases such as certain cancers,
hypertension and diabetes (Tecco, 2017). 
Exercises can come in all forms, whether you enjoy swimming, yoga,
weight-lifting or even playing quidditch, each activity reaps its own physical
benefits when done in healthy amounts. Of all the exercises, however, the two
most popular forms are walking and running, which together, account for over
80% of all fitness activities (Forgione, 2015). 
These similar exercises are not only relatively easy to participate in,
but also highlight how the intensity in physical activity may vary. In this
way, adjusting the speed of walking and running as the independent variable for
this experiment, allowed the correlation between memory and the intensity of
exercise to be studied. 

            The intent of this experiment is to identify the
relationship between the intensity of exercise and memory, or more
specifically, explicit semantic memory in Homo
sapiens.  Explicit memory is a form
of long-term memory that relies on conscious thought, and involves an intentional
effort to remember something.  Semantic
memory is a subset of explicit memory that deals with the recall of facts,
concepts or other general information. 
There is some debate on the area of the brain which stores these
memories, however, many believe it can be found in the hippocampus and cerebral
cortex (“Explicit Memory”, 2015). 
In order to understand any effect that exercise has on memory, it is
important to understand how these explicit semantic memories are naturally
formed.  Memories are formed by the
persistent changes in the strength of connections (synapses) between neurons,
also known as synaptic plasticity. 
Neural connections can be made stronger or weaker depending on how often
they are activated. Strengthening of synapses is caused when signals (action potentials)
are sent through connections regularly,  causing the post-synaptic cell to traffic  more for receptors for neurotransmitters on
its surface and thus making more easily activated by the pre-synaptic cell the
next time the memory needs to be recalled. For example, in the infamous
experiment with Pavlov’s dog, when Pavlov rang the bell, the dog would
immediately salivate because of his previous experiences of the bell ringing
and having received food. In this example, a strong synapse was formed between
the neuron responsible for the dog’s salivation and the neuron responsible for
hearing the bell so that once he heard the bell, the neuron for salivation was stimulated
as well.  This synapse is the dog’s
memory that a bell means feeding time. 
This process of strengthening and weakening synapses is known as long
term potentiation or LTP, and long term depression or LTD (“How are
memories formed?”, 2017).   

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            Human subjects involved in this experiment were treated
with utmost consideration and all necessary safety measures were taken to
prevent both physical and mental harm.  A
maximum speed of 9 mph for 2 minutes was given to subjects to prevent heart
attacks, dehydration and exhaustion as per the maximum speeds and durations
determined according to the subjects’ request. 
All subjects signed the informed consent form acknowledging the procedures
and safety considerations outlined within, including mandatory use of emergency
stop shirt clips when using the treadmill, use of proper footwear, proper
hydration etc (see appendix 1).

            As a high school student and life-long learner, I am
always looking for ways to improve memory to maximize my absorption of
information.  Since running and walking,
as forms of exercise are readily and easily available, the results of this
experiment will provide insight into the value of exercise before taking a test
or studying in order to improve my performance. 
Furthermore, as neuro-degenerative diseases become more prevalent in
society, like dementia, which caused 11.78% of deaths in the UK in 2016
(Dementia Deaths, 2016),  it is important
to identify the effect that exercise has on the formation and recall of
memories.  Understanding this correlation
is important in order to try and mitigate the risk of developing these
neurological diseases and for use as possible treatments to slow the
progression of memory loss.  In the
future I hope to further study this incredible topic and pursue a career as a
neuroscientist.From
the graph (Figure 1), an exponential function is obtained, which display, by
the curve, how the increase in percent change is not constant but increasing at
an accelerating rate.  This curve
represents exponential growth in terms of percent change, showing that the
higher the speed of running, the higher the increase in percent change of
memory test scores.              The results of the experiment did
support the hypothesis.  As hypothesized,
increasing the intensity of exercise led to an increase in memory test
scores.  Although the results showed an
exponential increase in percent change in relation to increased speed, overall
a positive correlation was identified as predicted.  However, if trials were conducted at higher
speeds, there would most likely be a plateau in the graph.  As the subjects run at increasingly high
speeds, they will eventually fall as a result of the speed, become exhausted,
faint, lightheaded, etc. and experience both mental and physical anguish
(Wedro, n.d.).  At this point, the memory
test scores would not increase in the same trend as the graph as the fatigue
and possible injuries from the high running speeds would cause a reduced
concentration or even inability to complete the memory test, and thus stray
from this positive exponential correlation. Despite the anticipation of such a
plateau, for the safety of the subjects, the maximum speed was determined by
all subjects to be one that was challenging and a high intensity speed whilst
being safely achievable without over exhaustion.

(Cornell, n.d.)

Figure
2: Bohr Shift

            Memories, as stated in the
introduction, are formed through the strengthening of synapses between neurons,
through the process of long term potentiation. 
The stronger the synapse, the more likely the synapse will be able to be
reactivated and the easier that memory will be recalled.  This synaptic strength is dependent on the number
of receptors on the post-synaptic cell to which neurotransmitters can bind; the
more receptors, the more likely the neuron will be activated by the
pre-synaptic cell (How are memories formed?, 2017).  In order to perform any cellular activity,
cellular respiration must occur in order to produce the required energy in the
form of adenosine triphosphate (ATP). Synthesis of the neurotransmitter
receptor proteins and neurotransmitters themselves, are no different.  As seen in the simplified equation for
cellular respiration,  Glucose + O2          CO2 + H2O +
ATP,  in order to produce the ATP needed for
synaptic plasticity, glucose and oxygen are essential (Nave, 2016).  Glucose is a monosaccharide that is absorbed
by the body and transported through the circulatory system where it can be used
by the body cells.  In order to keep
blood sugar levels at homeostatic levels, the pancreas secretes insulin to
convert blood glucose into glycogen in the liver when levels are high. Oppositely,
when the levels are too low, glucagon is secreted to convert glycogen back into
blood glucose.  When running, the body
cells, especially muscle cells, require more glucose for cellular respiration
and thus, more glucose is needed in the blood stream.  This stimulates the release of glucagon from
the pancreas to increase blood glucose levels for use by the muscles, but also
other cells such as the brain, allowing them to better form synapses (Allott,
2014). Furthermore, oxygen is taken into the body via the lungs and transferred
to the blood stream where it is transported by the hemoglobin protein in red
blood cells.  When running, the somatic
cells, undergo mass cellular respiration and thus, create carbon dioxide as a
by-product.  This carbon dioxide travels
in the blood by reacting with water to form hydrogen ions, thus lowering blood
ph.  Special chemoreceptors in the
medulla, detect this low ph and in response, send signals to the heart and
intercostal muscles to increase contraction/relaxation rate, thus increasing
breathing and heart rate (Allott, 2014). 
This increase in breathing rate that was observed in the subjects at
high running speeds, increased the amount of oxygen being brought into the
lungs to meet the body’s increased oxygen demand.  Another phenomenon occurs as a result of this
low blood ph during exercise, known as the Bohr shift.  This trend can be illustrated by the graph
(Figure 2) which shows a change in oxygen dissociation as the blood ph
increases.  Because of the increased
hydrogen ions in the blood, the hemoglobin ionizes and changes shape, reducing
its affinity for oxygen molecules, allowing more oxygen to leave the hemoglobin
and enter the cells that need it such as muscles or neurons.  Moreover, as heart rate and blood pressure
increase during exercise,  the glucose
and oxygen rich blood can be circulated better and faster, allowing all cells
to have more reactants available for cellular respiration.              A hormone and slow-acting
neurotransmitter, called epinephrine or adrenaline is also released by the
adrenal gland during exercise.  This
fight-or-flight hormone causes vasoconstriction, dilation of air passages, and
reduces the body’s ability to feel pain (“adrenaline”, n.d.).  This allows the body to focus on the task at
hand without the muscle soreness and increases nutrient circulation.  However, if too much adrenaline is released,
the subjects can feel dizzy or lightheaded, and possibly more restless and
irritable, which is another reason a plateau or decline in memory would be
expected if the experimental speeds were to surpass 9 mph.             Exercise not only increases blood
and glucose levels, but also prompts the release of specific factors that
affect brain development directly.  The
release of brain-derived neurotrophic factor (BDNF) and endorphins help to
improve concentration, synaptic plasticity and neurogenesis.  A 1988 study by T. Zigova revealed that BDNF
activity increased the number of neurons in olfactory bulbs, and the
hippocampus and thalamus.  This suggests
that BDNF released during exercise can cause the proliferation of neurons and
also enhance neuron survival (Binder, 2004). 
Because of its effect on neurogenesis and synaptic strengthening in the
hippocampus, BDNF release caused an increased ability to form memories in the eperiment.  However, approximately 30% of European
Caucasians, have a “BDNF gene variant that hinders post-exercise BDNF
production” (“Your body on exercise”, 2013)  possibly causing different magnitudes of
percent increases based on this genetic trait. 
Overall, the results of the experiment support the hypothesis that
increasing the speed of running will increase the percent change in memory test
scores.  In similar experiments with
exercise and memory, similar results were obtained, such as the experiment
conducted by Yousif Astarabadi
at Saddleback College, which showed that the average number of sets remembered
by the subjects increased from 4.6 to 7.3 after exercise, showing a positive
correlation between exercise and memory. Evaluation:            Within the experiment, there were
certain systematic errors which occurred in addition to areas which could have
been improved upon. By improving these areas, a greater degree of data
precision could be achieved if the experiment was to be conducted a second
time.            The first source of error was the
selection of subjects for the experiment. 
Although many factors were controlled in order to reduce large
disparities between the subjects, some subjects reacted differently to the
exercise than others.  For example,
subject 2 who had an average of 10+ hours of high intensity exercise a
week  showed very few signs or increased
breathing rate, heart rate etc. when compared to subject 1 at the same
speeds.  This variation in fitness levels
caused the results to be skewed as it took less intensity for subject 1 to
increase breathing rate, undergo hormone release etc. than subject 2. As seen by
the large standard deviations values of the means, we see that the level of
fitness of each subject had an effect on the accuracy of the average and thus
the results obtained from them.  If
future experimentation were to take place, it would be beneficial to select
subjects based on more specific physical traits such as normal resting heart
rate, and have each subject participate in the same athletic conditioning
before the experimentation starts in order to increase athletic uniformity. For
more accurate results, instead of measuring intensity of exercise due to speed,
percent change in heart rate can be used as an indicator of how hard the subject’s
body is working to maintain homeostasis and relatively when hormones are
released.  This would provide much more
accurate means and overall better results on the effect of exercise intensity
on explicit semantic memory, as the effect of fitness levels will no longer
exist.            In addition to the subject
selection, the environmental conditions in which subjects were placed before
and during the tests that could have been improved upon to increase precision
of data.  Although subjects were placed
away from many distractions and triggers that could increase heart rate, blood
pressure etc. or cause distractions, there were still many factors that were
unaccounted for (e.g. hallway sounds, movement and impatience etc).  These distractions could have caused a
decrease in concentration for some of the tests resulting in mistaken
correlations and percent changes thereby causing misguided observations.  In future experiments, using ear plugs or an
isolated, soundproof room will be beneficial in removing distractions in order
to isolate the effect of only the exercise on memory.            Moreover, subjects had different
eating schedules which could have caused skewing of the results.  Since some subjects had eaten only 10 minutes
before exercising, the food in their stomachs could have caused indigestion
problems or feelings of nausea that affected their concentration when taking
the memory test.  Furthermore, a subject
had not eaten anything the whole day, and this could have caused abnormally low
blood glucose levels that would not be able to respond to the exercise with the
same degree as someone who had eaten prior. 
In future experiments, the diets and timing of meals should be arranged
in order to ensure that the same nutrients are provided at the same time for
each subject to prevent indigestion or low glucose.            In order to improve the
experimentation for further research, testing more different independent
variable values would be recommended.  By
only testing increments of 2 mph, there was not enough information to formulate
a strongly supported trend line.  The
more independent values that are tested, the more data points can be plotted,
illustration the percent changes in memory test scores with increased
accuracy.  If the experiment was
conducted again, it would be ideal to change running speeds by 1 mph or if possible,
0.5 mph  to maximize accuracy.

            If these areas are improved upon in
further exploration, any data that is collected, will be more accurate.  In turn, any conclusions that can be drawn up
from the data received, will also be more accurate.