Grant Kovich
BIOL142, Section 021
TA: Brenna Hill
Exercise Physiology Lab Report
2 December 2011
The VO2 Max Test: An Indicator of Cardiovascular Fitness, Not Just for Athletes
Introduction
Exercise—considered to be stress relief by some, and torture by others. Many people are so
concerned with their appearance and surroundings during exercise, they do not realize the incredible
amount of activity that is happening physiologically in every cell of the body. Cardiovascular fitness can
be measured by performing a test called a VO2 max test, in which a subject’s body is pushed to the limits
of exercise, usually causing complete exertion. Although the main objective of the VO2 max test is to
determine how physically fit an individual is, the test also measures many vital physiological changes
throughout the body. Results from a VO2 max test can also provide insight to doctors who are pursuing a
treatment plan for a patient suffering from cardiovascular or respiratory diseases, by showing if the
treatment is effective or not. By recording these physiological changes as exercise intensity progresses,
biologists can understand how the systems of the body compensate for an increased demand for oxygen
and energy over time.
The VO2 max test is marked by stages, with each stage having increased exercise intensity, which
demands more output from the subject. When the body begins to undergo the process of exercise, many
physiological changes occur. Body temperature, respiratory rate, heart rate, and blood concentration of
both oxygen and carbon dioxide must change in order to maintain a homeostatic environment in the body
throughout exercise (1). As the intensity level of exercise increases, these changes are more pronounced.
From both personal experience and observed patterns of behavior from athletes, we feel that there
are many noticeable changes that occur during increased intensity exercise. Differences in various
physiological indicators can be seen when the body is at rest, during warm up, throughout exercise, and
during recovery. We expect to see changes in heart rate, exhaled tidal carbon dioxide concentration,
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oxygen concentration of exhaled air, body temperature, hemoglobin saturation, and mean arterial
pressure.
At rest, we expect the values for the physiological indicators to be at fairly normal levels i.e. body
temperature of 37ºC, heart rate of 55-65 BPM, etc. During the warm up period, as the body is rapidly
adjusting to exercise, we expect that all of the values will increase, in order to adjust to the physiological
stress that is occurring. We feel that all of the values except hemoglobin saturation will increase linearly
with an increase in exercise intensity, due to the body requiring more resources to adapt to a higher level
of exercise intensity. We predict hemoglobin saturation will decrease linearly in response to increased
exercise intensity, due to faster blood flow preventing hemoglobin stability in the blood. When exercise
capacity has been reached, and the subject cannot perform at a high level anymore, we feel that the values
will be at their highest levels, since the body will be at complete exhaustion. As the body recovers from
intense exercise, we expect the values to slowly decrease as the time for recovery increases, with the
exception of hemoglobin saturation, which we predict to slowly increase back to normal levels. However,
we feel that the values will not return to the same levels during rest prior to exercise until a few hours
after exercise. We believe that since high intensity exercise is extremely stressful on the body, it will take
more than a few minutes for complete recovery to occur.
Method
Subjects were chosen on a volunteer basis, and were only allowed to participate in
experimentation if they were in a completely healthy state. Prior to experimentation, age, height, weight,
gender, and whether or not the subject smoked were recorded for each subject. Exercise heart rate was
also calculated for subjects, by determining 80% of their maximal heart rate, which is calculated by 220 –
age. Subjects were connected to a polar heart rate monitor and a skin thermometer prior to exercise, so
that heart rate and body temperature could be measured throughout exercise. If at any point the subject’s
heart rate surpassed the exercise heart rate, experimentation would be stopped immediately. Initial
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measurements of tidal volume (spirometer), oxygen concentration of exhaled air (oxygen analyzer),
exhaled tidal carbon dioxide concentration (capnometer), hemoglobin saturation (pulse oximeter),
respiratory rate (capnometer) and blood pressure (sphygmomanometer) were taken while the subject was
at rest. Resting measurements, taken between 0 and 3 minutes, served as control measurements upon
which comparisons of the results of the experiment could be made.
Subjects were given 1-2 minutes to adjust to the treadmill, and then experimentation began. The
experiment consisted of exercise levels of increasing difficulty. Every three minutes, measurements of
heart rate, tidal volume, respiratory rate, exhaled total carbon dioxide concentration, and oxygen
concentration of exhaled air were recorded, just prior to moving onto the next stage of exercise. Visual
observations concerning the subject’s appearance were also recorded regularly, as safety was of the
utmost importance for the duration of the experiment.
When subjects could no longer move onto the next stage of the test, researchers ended the test by
lowering the treadmill speed to 3-4 miles per hour and lowering the treadmill angle to 0 degrees.
Measurements of skin temperature, hemoglobin saturation, and blood pressure were taken as soon as the
test ended. Subjects were then instructed to walk on the treadmill for no fewer than 6 minutes. At each
3-minute interval of the recovery period, measurements of heart rate, tidal volume, respiratory rate,
exhaled tidal carbon dioxide concentration, oxygen concentration of exhaled air, skin temperature,
hemoglobin saturation, and blood pressure were taken. At the conclusion of the recovery period, no
further measurements were taken, and final visual observations of the subject’s appearance were made.
Upon completing measurements of exhaled tidal carbon dioxide concentration, oxygen
concentration of exhaled air, and blood pressure, further calculations were performed to determine carbon
dioxide clearance, oxygen consumption, and mean arterial pressure, respectively. Carbon dioxide
clearance, the amount of carbon dioxide being expelled by the body every minute, was calculated by the
following formula: CO2 Clearance = (%CO2 of Exhaled Air) x (Tidal Volume) x (Respiratory Rate) (1).
Oxygen consumption, the amount of oxygen used by the body cells every minute, was calculated by the
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following formula: O2 Consumption = (%O2 of Exhaled Air) x (Tidal Volume) x (Respiratory Rate) (1).
Finally, mean arterial pressure, the average arterial pressure during a single cardiac cycle, was calculated
using the following formula: MAP = Diastolic Pressure + 1/3(Systolic Pressure – Diastolic Pressure) (2).
Results
Figure 1. Observed changes in heart rate with increasing exercise intensity.
Heart Rate (BPM)
250
200
150
Subject 1
100
Subject 2
50
0
0
5
10
15
20
25
Time (min)
Heart rate increased rapidly as exercise began, slowly increased throughout exercise, and drastically
decreased at the end of exercise. It did not, however, reach resting levels prior to exercise in both
subjects.
CO2 Clearance (L/min)
Figure 2. Observed changes in CO2 clearance with increasing exercise intensity.
2.5
2
1.5
1
Subject 1
0.5
Subject 2
0
0
5
10
15
20
25
Time (min)
Carbon dioxide levels fluctuated as exercise began, and then increased throughout exercise. At the
completion of exercise, levels sharply declined and were very close to the resting levels seen at rest.
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O2 Consumption (L/min)
Figure 3. Observed changes in oxygen consumption with increasing exercise intensity.
1.2
1
0.8
0.6
Subject 1
0.4
Subject 2
0.2
0
0
5
10
15
20
25
Time (min)
Oxygen consumption gradually increased at the beginning and throughout exercise, with variation
occurring at the end of exercise. Post-exercise levels varied among the subjects, being above and below
resting levels.
Table 1. Observed changes in body temperature, hemoglobin saturation, and mean arterial pressure with
increasing exercise intensity. Time points correspond to the following periods: rest = 0, warm up = 3
minutes, exercise = 18 minutes, and recovery = 21-24 minutes.
Time (min) Body Temperature (ºC) Hemoglobin Saturation
Mean Arterial Pressure
(%)
(mmHg)
Subject 1
Subject 2
Subject 1
Subject 2
Subject 1
Subject 2
0
34
35
98
97
77
85
3
35
35
100
96
77
87
6
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Due to the manner in which these measurements were made, we felt it was unsafe to
record measurements while the subjects were performing the experiment.
12
15
18
37
36
79
84
107
113
21
36
36
86
96
103
83
24
36
37
95
96
80
78
Body temperature increased slightly at the onset of exercise in both subjects, increased significantly
during exercise, then failed to return to resting levels at the conclusion of exercise. Hemoglobin
saturation varied when exercise began, drastically decreased during exercise, then gradually increased
back to near normal levels during the recovery period in both subjects. Mean arterial pressure in both
subjects increased slightly as exercise began, increased at a higher rate as exercise took place, and then
slowly lowered to levels comparable to those seen during the resting period.
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Overall, observed data featured a similar trend in that during rest, measurements were low, and
gradually increased as exercise commenced. As exercise intensity increased, most of the data increased
in response to intensity. At the conclusion of exercise, during the recovery period, most of the data
lowered in values, returning to levels near what they were prior to exercise. In the case of hemoglobin
saturation, the data showed an opposite trend—values were normal at resting levels, decreased with
increasing exercise intensity, and then increased back to near normal levels during recovery.
Discussion
Prior to experimentation, predictions were made about how the following physiological factors
would change with exercise of an increasing intensity: heart rate, carbon dioxide clearance, oxygen
consumption, temperature, hemoglobin saturation, and mean arterial pressure. A general hypothesis was
made for all physiological tests--normal levels prior to exercise, a linear increase in levels during
increased exercise intensity, and a slow decline back to near resting levels during recovery, while the
opposite trend was predicted with hemoglobin saturation.
Heart rate displayed by the subjects followed a pattern that which strongly supports our
hypothesis. During the warm up period, heart rate slowly increased as the body adjusted to exercise. As
exercise intensity increased, heart rate also increased linearly to allow for more blood flow, fulfilling the
requirement of a larger need for oxygen and removal of carbon dioxide in the muscles. During recovery,
heart rate slowly declined to levels that were slightly higher than those seen during rest prior to exercise
(Fig. 1).
In theory, the results for carbon dioxide clearance and oxygen consumption are dependent on
each other. If the muscles are consuming more oxygen, this means that carbon dioxide is produced at the
same rate, signifying the need for more rapid removal from the muscles. Our results do not strongly
support our original hypothesis, as the measurements fluctuated throughout the experiment (Figs. 2 & 3).
We feel that the outlying measurement at 10 minutes is a possible source of error, due to the fact that
exercise intensity increased, not decreased, from 5 to 10 minutes. The extremely low values at 20
minutes, and the fluctuations that occurred in Subject 2 between 15 and 20 minutes are also erroneous in
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our opinion, because exercise intensity was still increasing during this time (Figs. 2 & 3). Carbon dioxide
clearance and oxygen consumption should increase linearly with exercise intensity, as the body requires
more oxygen and needs to remove more carbon dioxide when muscles are performing greater work. We
feel that the source of error behind these outlying measurements is the method in which oxygen
consumption and carbon dioxide clearance were measured. Since the nose was not clipped during
experimentation, subjects expelled air through both the nose and mouth. This signifies that complete
exhalations were not being sent through the sensors, because some of the air was expelled through the
nose. We believe that a larger volume of air being expelled through the nose, rather than the mouth
caused the outlying data points. We predict that had the nose been clipped during experimentation, the
results would have corresponded with our hypothesis.
At the beginning of exercise, body temperature increased, just as when exercise intensity
increased, which strongly supports our hypothesis. However, during recovery, body temperature dropped
very slightly, and measurements were different for both subjects, which does not very strongly support
our hypothesis (Table 1). We do not feel that this is a source of error, but rather a physiological
difference in each subject. The rate at which body temperature is lowered can depend on many factors
including the amount of clothing the subject is wearing, the temperature of the exercise environment, and
the amount of fluid intake during recovery, and the cardiovascular fitness level of the subject. We believe
that it can take upwards of 30 minutes for body temperature to return to levels seen prior to exercise.
Overall, the observations seen when measuring body temperature follow a similar pattern to what we
hypothesized; body temperature just did not decline as much as we would have expected during the
recovery period.
The results for hemoglobin saturation can be related to the changes in heart rate. As exercise
intensity increases, heart rate also increases, sending more blood to the muscles. This causes less
hemoglobin molecules to stay together in red blood cells, which lowers hemoglobin saturation. We
predicted that levels would drop linearly with increasing exercise intensity, and then return to normal
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levels during recovery. Hemoglobin saturation observed throughout experimentation did in fact strongly
support our hypothesis, due to the fact that an increased heart rate caused lower hemoglobin saturation.
Since mean arterial pressure is calculated from diastolic and systolic pressure, and there is a
relationship with heart rate and blood pressure, we predicted that mean arterial pressure would increase
with increased intensity of exercise, and then decrease back to levels seen during rest prior to exercise.
Due to the heart pumping a greater volume of blood at a faster rate, blood pressure must increase as a
result of these changes. Blood pressure measurements allowed for mean arterial pressure to be calculated,
and it can be seen in the results that mean arterial pressure did in fact strongly support our hypothesis
(Table 1).
Conclusion
The aforementioned experiment displayed data that is extremely valuable in not only determining
the cardiovascular fitness of an individual, but the different physiological changes that occur during
exercise as well. Data can not only be used to assess the cardiovascular fitness from an athletic
standpoint, but also to compare individuals who suffer from respiratory diseases such as asthma, COPD,
and emphysema, as well as cardiovascular diseases such as hypertension. We feel that with more
advanced equipment our measurements could have been more precise. We also believe that more
frequent measurements would have allowed for more consistent data. However, with the resources at
hand, we feel that experimentation went smoothly, and valuable data was collected and analyzed.
Although all of our hypotheses were accepted, we feel that changes can be made to allow the
experiment to run more smoothly and provide more valuable data. We feel there should be three groups
of subjects sorted by their activity level--sedentary, moderately active, and very active. With a random
sample of a larger subject pool, correlations and comparisons can be made not only within each group,
but among the groups as well. Also, our experiment featured only women subjects. For a complete
experiment, subjects can also be separated by gender. Valuable insights into exercise physiology can be
drawn from a comparison of the physiological changes that occur across different activity levels. We feel
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that this experiment was a step in the right direction, and future studies concerning exercise physiology
will only yield more exciting and significant findings.
References
1. Waters J. 2011. Exercise Physiology Handout: https://cms.psu.edu/Merge/2009/MRG-110708152625-JRW8/_assoc/009D3BC2BF154BC081CCD6FAD577D7DB/exercise_physio.pdf.
2. Waters J. 2011. Heart Sounds and Blood Pressure Handout: https://cms.psu.edu/section/content/
default.asp?WCI=pgDisplay&WCU=CRSCNT&ENTRY_ID=3E29AB3B7FD74F1FAD552C99
EB191DBA.
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