Why is it so hard to lose fat? Because it has to get out through your nose! An exercise physiology laboratory on oxygen consumption, metabolism ...
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Adv Physiol Educ 45: 599–606, 2021.
First published June 1, 2021; doi:10.1152/advan.00006.2021
LABORATORY SOURCEBOOK
Why is it so hard to lose fat? Because it has to get out through your nose! An
exercise physiology laboratory on oxygen consumption, metabolism, and
weight loss
Edward K. Merritt
Department of Kinesiology, Southwestern University, Georgetown, Texas
Abstract
Exercise is thought to be an effective means to quick weight loss. However, few people have realistic exercise-induced weight
loss expectations. Fewer understand how weight is “lost” and where the lost mass goes. Understanding that fat is “burned” with
inhaled oxygen and most of the mass lost must be exhaled as carbon dioxide might help individuals create realistic weight loss
expectations. The purpose of this laboratory activity is to 1) provide students with a basic understanding of the role of oxygen in
fuel metabolism during physical activity and its relationship to energy expenditure and mechanical work, and 2) engage students
with collection of their own data to determine a realistic timeframe for exercise-induced weight loss. In the prelaboratory, ques-
tions such as, “When you lose weight, where does it go?” are asked. A guided discussion helps students understand the basic
biochemistry required for weight loss. For the activity, students complete walking or running exercise, recording the time and
distance. The relationship of exercise to physics’ concepts of mechanical work and energy utilization are discussed with the con-
cept of “calorie burn” and its relationship to oxygen consumption. Students estimate oxygen consumed and calories burned dur-
ing exercise using established metabolic equations. Finally, the amount of energy (i.e., calories) equivalent to 1 pound of fat is
discussed. Students calculate how long he/she would have to exercise to burn 10 pounds (4.5 kg) of fat. A person of average
size and fitness, needs 60 þ h of exercise to burn 10 pounds of fat. Supplementary activities including a dramatic gummy bear
oxidation and the use of a metabolic cart reinforces these concepts and validates the laboratory estimates.
carbon dioxide; metabolism; oxygen consumption; physical activity; weight management
INTRODUCTION science students in introductory biology courses fared
better than in the study of Meerman and Brown; however,
Objectives and Overview misconceptions were prevalent (8). By simplifying the
complexities of negative energy balance to the visceral
Despite the many health benefits of increased physical ac-
description that most lost fat mass is exhaled through the
tivity (1), well-established scientific evidence proves that
nose and mouth, perhaps students and future health care
substantial weight loss is not likely in most individuals hop-
professionals will have more realistic expectations for
ing to lose weight through physical activity alone (2). Despite
exercise-induced weight loss and understand that life-
the scientific research, daily physical activity and exercise
style changes in both dietary and physical activity habits
programs are often believed to be an effective method for
are most important. Therefore, the purpose of this labora-
overweight individuals to quickly lose substantial fat mass.
tory activity is to 1) provide students with a basic under-
Surveys of various populations, including college students,
standing of the role of oxygen in fuel metabolism during
indicate that 30–90 þ % of individuals consider exercise,
physical activity, and its relationship to energy expendi-
even more so than dieting, an effective weight loss strategy
ture and mechanical work, and 2) engage students with
(3–6). Possibly contributing to the misconception of exercise
collection of their own data to determine a realistic time-
as a powerful weight loss treatment is that few people under-
frame for exercise-induced weight loss.
stand that excess fat is “lost” from the body in the form of
carbon dioxide and water. Surprisingly, a survey of 150 medi-
Background
cal and health professionals by Meerman and Brown, deter-
minedUNDERSTANDING EXERCISE WEIGHT LOSS WITH METABOLIC EQUATIONS
In a simplistic breakdown for understanding of this les- capitalizing on student understanding of heart rate and
son, the human body is the mass. Moving the human body exercise is beneficial to understanding this lesson.
over a certain distance is mechanical work. A larger body
requires more force to move and moving a body over a lon- Learning Objectives
ger distance requires more work. Therefore, a 70-kg individ- The following learning objectives include both content
ual running a marathon (42 km) performs more work than a knowledge and process skills in one list.
70-kg individual running a 100-m race does. After completing this activity, the student will be able to
Work, including all physical activity, requires energy. do the following:
This relatively simple physics concept governs the human 1. CONTENT KNOWLEDGE: Explain the relationship
body’s ability to exercise and explains why we need to eat between body movement, the consumption of oxygen,
food for fuel and store it. The more mechanical work per- and energetic demand.
formed, the more energy required. Therefore, the mara- 2. CONTENT KNOWLEDGE: Describe the basic biochemi-
thoner needs more fuel than the 10-m runner does. As cal reaction of glucose and fatty acids with oxygen to
food is fuel, and in the United States the fuel energetic produce carbon dioxide and water.
unit on nutrition labels is the calorie (calorie = 1 kcal = 3. PROCESS SKILLS: Estimate oxygen consumption and
4.184 kJ), the marathoner “burns” more calories than the calorie burn during physical activity using established
100-m runner. In the body, and specifically within the metabolic equations.
forcefully contracting muscles accelerating and moving 4. PROCESS SKILLS: Calculate and set realistic exercise-
the runner’s body mass with each step, the fuels from food based weight loss goals.
are broken down (oxidized). During aerobic exercise, the
primary fuels oxidized are carbohydrates (glucose) and Activity Level
fats (fatty acids). The oxidation of these fuels is accom-
Initially designed for kinesiology undergraduates in exer-
plished using oxygen delivered to the muscles from the
cise physiology and physical assessment type courses to gain
cardiorespiratory system. The basic chemical reactions
an understanding of the principles of the direct measure-
utilize oxygen to break down the fuels, producing carbon
ment of oxygen consumption and carbon dioxide production
dioxide, water. The reactions also release energy, captured
to determine cardiorespiratory fitness, this activity is suita-
in the human body in the form of adenosine triphosphate
ble for students with interest in general sciences or health
(ATP), which the muscles use to perform contractions, as
(e.g., biology, anatomy, and physiology, chemistry, etc.). As
follows:
described, the laboratory can be completed using equipment
Oxidation of glucose: C6H12O6 þ 6 O2 ! 6CO2 þ 6H2O þ
and resources available in most undergraduate kinesiology
energy
or physiology programs, but modifications can be made to
Oxidation of the fatty acid palmitate: C16H32O2 þ 23 O2 !
complete a version of the activity using any basic classroom.
16CO2 þ 16H2O þ energy
Additional modifications make this activity suitable for high
The carbon dioxide produced in these reactions is trans-
school students or any average adult.
ported through the blood to the lungs and ultimately
exhaled. The runners used oxygen to breakdown fuels stored Prerequisite Student Knowledge or Skills
in the body, which means they were a part of the mass of the
body, and therefore, because the marathoner did more me- Before doing this activity, students should have a basic
chanical work and broke down more fuel to do it, the mara- understanding of high school-level science and a basic
thoner used the most oxygen. The carbon molecules, which understanding nutritional calories.
were a part of the stored fat or glucose molecules, have now Time Required
been exhaled in the carbon dioxide and their mass has left
the body. Therefore, the marathoner has lost the most mass The entire laboratory activity with prelaboratory dem-
during exercise. Ultimately, these relationships mean that onstration, discussion, exercise activity with metabolic
the amount of oxygen utilized is proportional to the amount calculations, and direct measurement of respiratory gas
of mechanical work performed, which is proportional to the composition during exercise requires 2–3 h of student-
amount of mass lost. These relationships are explored in this contact time with an additional 30 min before and after for
laboratory activity through a prelaboratory demonstration of equipment set-up and clean-up. Modification of the activ-
the oxidation of glucose, a walking/running exercise to ity with a shortened, video prelaboratory and elimination
determine oxygen consumption and calorie burn, and dis- of the respiratory gas measurement aspect requires only
cussion of weight loss due to exercise. Because of the wide- 45–60 min of student-contact time.
spread understanding of heart rate as a measure of
exercise intensity, most students already have a baseline METHODS
knowledge that allows them to understand the more com-
plicated nature of the metabolic and physiologic relation- In the sections below, the full laboratory activity is
ships in this lesson. While heart rate is less tightly coupled described as it is intended to be reproduced for undergradu-
to oxygen consumption than oxygen consumption is to ate kinesiology students, but aspects that can be eliminated
energetic demand (e.g., if two people are exercising at a to save time or modified for different audiences are noted
heart rate of 150 beats/min, one might be walking and the with “(optional).” Educators who adopt this activity should
other running, but if two people have an oxygen consump- know and conform to their institutional guidelines regarding
tion of 2 L/min, they are both burning 10 cal/min), data collection data from human participants.
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Equipment and Supplies Students are instructed to read the nutrition label and ingre-
dients and think about what happens when they eat one.
Part 1b: prelaboratory demonstration (optional). Most individual gummy bears are 6–10 cal and composed of
• Gummy bear or similar type candy with high sugar various sugars, gelatin, and colorings. A short (25-mm outer diameter, >100-mm What do you have to do? How long does it take?”
height, ability to withstand temperature of 400 C)
• Ring stand with test tube clamp with ability to with-
The instructor then tells the students that the calories in
stand temperature of 400 C
the gummy bear are going to be released and visualized. The
• Burner or propane torch to melt NaClO3
following steps are part of the classic “Death of a Gummy
• Crucible tongs or long forceps >20 cm, for inserting
Bear” experiment:
gummy bear in test tube
1. In a well-ventilated outdoor area or under a fume hood
• Chemical fume hood or large outdoor space
indoors, set up a test-tube in a stand over a burner.
2. Put 5–10 g of NaClO3 in the test tube and heat it until it is
Part 2: exercise and classroom activity.
molten
• Participants should be wearing clothing suitable for
3. Turn off and remove the burner.
low-to-moderate intensity exercise
4. With tongs or long forceps, drop the Gummy Bear into
• Walking/running track or other area of known distance
the NaClO3 and move away quickly. The reaction will
suitable for exercise
start instantaneously with flames and gases rapidly
• Stopwatch
forming and blowing out of the top of the test tube for
• Calculator
upwards of 1 min depending on the gummy bear size
Part 3: respiratory gas analysis during exercise and composition.
(optional). 5. Allow the reaction to proceed until no obvious flames or
• Stationary metabolic cart or other portable device for gases are being released. The test tube and remaining
metabolic analysis of respiratory gases [a system that residue will remain hot and unsafe to handle for several
measures ventilation volume and percentage of expired minutes.
oxygen content to determine volume of oxygen con- Immediately following the demonstration, ask students to
sumption (V_ O2) is needed for the calculations]; exam- write down the reactants and products. For ease of under-
ple systems: Parvo Medics TrueOne 2400 (Salt Lake standing, the reaction can be simplified to the reactants; glu-
City, UT) and PNOE Portable Metabolic Analyzer (Palo cose and oxygen (liberated from NaClO3 during heating by
Alto, CA) burner); and products: carbon dioxide, water, and heat as fol-
• Nonrebreathing mask or mouthpiece that allows partici- lows:
pant to inhale room air while collecting/analyzing
exhaled air C6H12O6 þ O2 ! H2O þ CO2 þ energy (heat)
• Treadmill (if using portable metabolic analyzer, the area
of known distance can be used) Following a brief discussion about the reactants and prod-
ucts, the instructor draws the connection of the reaction wit-
Instructions nessed, to the basic reactions of food eaten being stored as
Part 1a: prelaboratory questions. energy that is used to fuel daily activities emphasizing that
Students are asked to answer the question: oxidation of fat is similar to that of glucose as follows:
“When you lose weight, where does it go? Literally, C16H32O2 þ 23 O2 ! 16 CO2 þ 16 H2O
where is the mass that was lost?”
Returning to the first question before the demonstration,
students should be guided to the conclusion that most mass
Part 1b: prelaboratory demonstration (optional). lost is actually exhaled as carbon dioxide. A subsequent
The prelaboratory activity is a classic chemistry demonstra- question that can be asked, but does not have to be answered
tion of the oxidation of carbohydrates to carbon dioxide (CO2) because it is supposed to highlight the difficulty of weight
and water (H2O). Sometimes called the “Death of a Gummy loss by exercise alone with no dietary modifications is:
Bear,” this concept is taught in many general chemistry
undergraduate courses and the chemistry and methodology is “How much does one breath weigh?”
well described in the educational literature (9). In place of the
in-person demonstration for those without the resources or to
save time, numerous videos are publicly available online that Part 2: exercise and worksheet activity.
are suitable for classroom viewing (10). Before the demonstra- After Part 1a: prelaboratory questions, if the students did not
tion, bags of gummy bears are distributed to the class. see the Gummy bear demonstration, a brief discussion is
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necessary so they understand the basic chemistry of glucose Medicine updated and revised the equations that allow cal-
and fat oxidation to release energy and exhale carbon diox- culation of relative volume of oxygen consumption based on
ide as follows: speed of walking or running and %grade of surface (e.g., 10%
grade = 0.1) (13) as follows:
Oxidation of glucose: C6H12O6 þ 6 O2 ! 6CO2 þ 6H2O
Walking: V_ O2 = 0.1 ____m/min þ (1.8 ___m/min
Oxidation of fatty acid palmitate: C16H32O2 þ ___grade) = ______ml·kg1·min 1
23 O2 ! 16CO2 þ 16H2O
Running: V_ O2 = 0.2 ____m/min þ (0.9 ___m/min
Students then watch a commercial or view an advertise- ___grade) = ______ml·kg1·min 1
ment for a popular fitness/exercise product. The commercial
or advertisement needs to discuss calorie burn and weight Returning to the worksheet, students calculate step 5 to
loss. At a minimum, the advertisement should provide data determine the relative oxygen consumption rate required for
on calories burned using the equipment or how much weight the pace they walked or ran. The instructor confirms with
a person can expect to lose using it along with information the class that the higher relative oxygen consumption rate is
on how often and for what duration/session a person needs by students who ran the farthest. Since the equations pro-
to exercise on the product. Examples abound; however, most vide relative V_ O2 (milliliters of oxygen used per minute for
Bowflex Treadclimber (Nautilus Inc., Vancouver, WA) com- every kilogram of the individual’s body mass), step 6 on the
mercials available online contain data and information for a worksheet calculates each individuals’ absolute V_ O2. A brief
complete analysis (11). discussion on why mass affects oxygen consumption is
The instructor guides a short discussion of the advertise- made obvious by the fact that if oxygen use is proportional
ment’s claims. For example, asking students if it would be to mechanical work, which is the product of force and dis-
possible to burn over 600 cal in 30 min and what 45 pounds tance, then a larger person needs to produce more force to
(20.5 kg) of weight loss in 3 mo actually means in terms of move their mass a certain distance. Identifying students in
exercise frequency, intensity, and duration. Introduction of the class with similar pace, but differing masses highlights
several simplified concepts from chemistry, physics, and this concept. After calculating step 6, students turn over the
physiology follows the discussion. Whether they reach them worksheet.
on their own or with instructor guidance, the following sim- The chemistry of glucose and fat oxidation is briefly revis-
plified relationships are critical for students to understand: ited. In-depth understanding of the stoichiometry of the
• The physics’ concept of mechanical work (force dis- reactions is not necessary, but simplifying the concept is
tance) applies to humans: moving a mass (body mass) necessary so students understand that 5 cal of a fuel is oxi-
requires force and the further it is moved, the higher the dized for every liter of oxygen consumed. Students calculate
work. step 7 to find calories burned per minute based on oxygen
• Mechanical work performed is proportional to energy consumption per minute. After calculating step 7, students
(calories) utilized. turn over the worksheet.
• Energy utilized is proportional to fuels burned. A brief summary is provided of the “Physical Activity
• Based on the above chemical reactions, burning more Guidelines for Americans” recommendation for moderate
fuels requires more oxygen. intensity aerobic physical activity for 30 min or more most
• Cells using more oxygen must have had a delivery of days of the week (14). A discussion of these in light of health
oxygen and weight loss provides context before the students using
• If more oxygen is delivered, the heart must have deliv- step 8 to calculate how many calories they would burn in 1 h
ered more blood. if they maintained their exercise pace from the earlier activ-
• An increase in heart rate is generally indicative of an ity. After completing step 8, students turn over the
increase in oxygen utilization. worksheet.
• The amount of oxygen utilized is proportional to the The commercial/advertisement previously shown is revis-
amount of mechanical work. ited. Since they have now calculated their own calorie burn,
After clarification of these relationships, students exercise students have context with which to assess the advertise-
and complete a worksheet using their collected data to expe- ment’s claimed calorie burn. Data presented in the advertise-
rience the relationships themselves. ment are scrutinized and the instructor shows calculations
Students are instructed to walk or run for 5–10 min at a to determine V_ O2 from the company’s claims. For example, if
pace they could maintain for 1 h. This activity requires a a company claims a person can burn 612 cal in 30 min, the
track or segment of known distance. Upon completion of the calculation shows that requires 4.1 liters of oxygen per mi-
activity, students receive a worksheet (Fig. 1) to record their nute. Assuming the person has a mass of 70 kg, this would
distance and time. Completing steps 1–4 on the worksheet require them to exercise at a relative V_ O2 of nearly 60
calculates their speed in meters/minute. mL·kg1·min1. Displaying a table of maximal oxygen con-
After step 4, students turn over the worksheet so they do sumption norms and fitness categories proves that a V_ O2 of
not work ahead during the subsequent discussion. Based on nearly 60 mL·kg1·min 1 is only obtainable byUNDERSTANDING EXERCISE WEIGHT LOSS WITH METABOLIC EQUATIONS
Metabolic Calculations/Exercise Math Worksheet
1) How far did you run/walk?
1 lap = 200 meters Distance = _____________ meters
2) How long did the run/walk take you? Time = _____________ seconds
3) Convert your time to minutes (divide #2 answer by 60) Time = _____________ minutes
4) Calculate your speed (Distance in meters divided by time in minutes)
Speed = ______________ m/min
5) Calculate your VO2 by inserting speed into the equation (grade = 0):
Walking: VO2 = 0.1 x ______ m/min + (1.8 x _____ m/min x ___ grade) =_______ ml•kg-1• min-1
Running: VO2 = 0.2 x ______ m/min + (0.9 x _____ m/min x ___ grade) =_______ ml•kg-1• min-1
6) Convert your VO2 to ml/min:
a. Multiply VO2 from above by body mass (in kg)
2.2 pounds = 1 kg VO2 = _____________ ml/min
b. Convert your VO2 to L/min:
1000 ml = 1 L (divide 6a answer by 1000) VO2 = _______________ L/min
7) What was your rate of calorie burn?
1 liter of oxygen consumed = 5 calories burned
(Multiply 6b answer by 5) Energy burn = _________ calories/min
8) How many calories would you burn in 1 hour?
60 minutes = 1 hour (multiply answer #7 by 60) Energy burn = _________ calories/hr
9) How many pounds of fat would you lose per hour?
3,500 calories/1 pound of fat (divide answer #8 by 3500) Weight loss = __________ pounds/hr
10) How many hours would you have to exercise at that pace to lose 10 pounds of fat?
(Divide 10 by answer #9) To lose 10 pounds of fat = ______________ hours
What are the implications?!
Figure 1. Metabolic Calculations/Exercise Math Worksheet.
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well above that calculated and is in the range of elite endur- consumption calculations. Student volunteers can walk or
ance athletes. For this specific example, students realize that run on a treadmill (or track of known distance if a portable
the manufacturer’s claims are theoretically possible, even if analyzer is used) at the same self-selected pace they chose in
highly unlikely, but certainly not in the manner in which part 2 while oxygen consumption is measured. Students
they are depicted in the commercial by the actors: walking, should exercise at their pace for 10 min while collecting
happy, smiling, and sweat free. V_ O2 data. Using the last 5 min of V_ O2 data, students can cal-
The remainder of the worksheet and lesson focuses on culate calories burned and compare the measured V_ O2 and
exercise-induced weight loss. Having established that calo- calories burned to the metabolic equation estimates for that
ries are burned through exercise based on principles of pace.
physics and chemistry, students understand realistic calorie
burning goals during exercise but do not yet have the context Troubleshooting
of how calorie burn and weight-loss are related. A classic Part 1: prelaboratory activity.
nutrition review by Wishnofsky (16) is briefly discussed. Common problems experienced during the gummy bear
Wishnofsky concluded that 3,500 cal are equivalent to 1 oxidation reaction prevent the reaction from completing
pound (0.45 kg) of body mass. Subsequent research deter- or involve safety issues with the flames and heat given off
mined that this estimate might be overly simplified and up by the reaction. To ensure a complete reaction, melt the
to 10% too low; however, for this activity the conceptual idea NaClO3 completely before addition of the gummy bear. At
is more important than specific scientific details that would room temperature, the NaClO3 is a solid crystalline sub-
require much more comprehensive student understanding stance but when melted completely will appear as a clear
of biochemistry. Utilizing Wishnofsky’s estimate, students liquid. The heat of the molten NaClO3 can melt the
use step 9 to calculate how much weight they would lose if gummy bear and cause it to stick to the tongs or the side
they continued exercising at that pace for an hour. Step 10 of the test tube, preventing the gummy bear from sub-
asks them to calculate how many hours they would have to merging in the reactant. To avoid this, the test tube diam-
exercise to lose 10 pounds (4.5 kg). The instructor should eter should be at least 25 mm and the gummy bear should
confirm student answers and guide a discussion with ques- remain far from the heat and then quickly dropped into
tions similar to those below: the reactant with the tongs.
• What are the implications for the average person: some-
one of average body mass and fitness? Part 2: exercise and worksheet activity.
• What are the implications for an obese, sedentary per- Metabolic equations estimate oxygen consumption during
son: someone with excess fat mass and below average steady-state aerobic exercise. To achieve steady state
fitness? exercise, instructing the participant to “walk or run for 5–
• If an unfit person, who has never exercised regularly, 10 min at a pace that he or she might be able to maintain
meets the “Physical Activity Guidelines for Americans” for 1 h” usually provides reasonable estimates of oxygen
by exercising 30 min per day for most days of the week consumption. The calculations will not be accurate if the
for 1 mo, what will you tell them if they complain about participant exercises at a higher exertion level, and the
having not lost weight? inaccuracies will be apparent during part 3 of the labora-
• How might a once per month celebratory meal for regu- tory. Additionally, depending on the educational level of
larly exercising mean for an individual’s weight loss the students, extra guidance on calculations and unit
goals? conversions beyond that already provided on the work-
To provide greater context for the difficulty of exercise- sheet might be necessary.
induced weight loss, the instructor should highlight that a
person of average weight and fitness needs 60 þ h (2 mo Part 3: respiratory gas analysis during exercise.
straight of daily 1-h exercise sessions at an uncomfortable in- Proper knowledge and training are necessary to utilize meta-
tensity) to burn 10 pounds (4.5 kg) of fat mass. Comparing bolic carts and analyzers appropriately. Common issues
these numbers to the recommended physical activity guide- experienced during this aspect of the laboratory involve
lines of 150 min/wk of moderate intensity activity should fur- improper calibration of the equipment or ill-fitting face-
ther reinforce the concepts, as students can calculate that masks/mouthpieces. Follow manufacturer’s instructions for
this would require more than 6 mo. To conclude the lesson, equipment set-up. Check that no air can leak out of the face-
students discuss how the metabolic equations can be used mask during normal exhalations by covering the exhalation
other than to determine calorie burn, including their utility opening and trying to exhale gently. For the V_ O2 measure-
in estimating maximal oxygen consumption in field-based ments and calorie calculations to be accurate and approxi-
cardiorespiratory tests and estimating pace for competitive mate the estimates from the metabolic equations in part 2,
endurance exercise performance. the V_ O2 measurements must be recorded during steady-state
exercise for a sufficient amount of time while accounting for
Part 3: respiratory gas analysis during exercise the concept of oxygen deficit. The oxygen deficit occurs dur-
(optional). ing the first 1–3 min of exercise when V_ O2 is lower than
With specialized equipment, including a metabolic cart or expected for the given pace of the individual. A simple way
portable metabolic analyzer capable of analyzing exha- to account for this is to have the participant exercise for
led gases, upon completion of the metabolic equations activ- 10 min total while measuring V_ O2 and ensuring the partici-
ity and worksheet, an optional addition to the laborat- pant’s respiratory exchange ratio stays below 1.0. Use only
ory can determine the accuracy of the estimated oxygen the last 5 min of data for the calculations.
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Safety Considerations Part 2: exercise and worksheet activity.
Allowing students to walk or run a specific distance they can
Oxidation of the gummy bear in the prelaboratory activity complete in 5–10 min (e.g., 1 km) while timing themselves
is an intense, exothermic reaction creating high tempera- simplifies the exercise portion of the activity. Most students
tures with visible flames and gases (mostly in the form of walking/running at steady state speeds will travel between
water vapor and carbon dioxide). Containing the reaction in 100–200 m/min and therefore should be in that range for
a fume hood or in a well-ventilated outdoor space behind a step 4 of the worksheet. Step 5 V_ O2 will therefore range from
protective barrier with no flammable materials nearby is 13.5 to 43.5 mL·kg1·min 1. Depending on individual stu-
necessary. The oxidizing agent, NaClO3 or KClO3, should be dent body masses, the numbers will vary greatly from steps
properly stored and the stock bottle should not be near the 6–10. For step 10, most students will calculate it would take
reaction. These oxidizing agents have the following Material between 30 and 90 h of exercise to lose 10 pounds (4.5 kg) of
Safety and Data Sheet warnings: Strong oxidizer. Contact mass. Using this activity for groups of sedentary older adults,
with other material may cause a fire. Causes eye and skin much lower numbers will be common. Regardless of the
irritation. May be harmful if swallowed. Causes digestive and group though, students nearly always react with incredulity,
respiratory tract irritation. May cause blood abnormalities. and sometimes frustration, at the amount of time it would
May cause kidney damage. May cause methemoglobinemia. take to lose weight through exercise. Instructors should
Personal protection equipment including eye protection, remember to emphasize the countless other benefits of phys-
gloves, and laboratory coat should be worn by anyone han- ical activity. Rarely is healthy weight loss achieved through
dling the chemicals or within 2 m of the reaction. exercise alone. Healthy lifestyle goals encompassing physi-
The reaction progresses rapidly, so the instructor should cal activity, appropriate food choices, and mental health out-
quickly move away after dropping the gummy bear. In some comes are essential for overall health and body composition.
cases, remnants of the gummy bear eject from the test tube
during the reaction. Do not touch the set-up until it has Part 3: respiratory gas analysis during exercise.
cooled completely after the reaction. Assuming that students’ self-selected walking or running
The activities of this laboratory can be completed with pace during the part 2 exercise was true steady-state exer-
light to moderate physical exertion, which is safe for most cise, data from the metabolic cart are within 10% of the met-
college undergraduates, but as with any activity that abolic calculation estimated V_ O2 for most students.
involves physical exertion, it is recommended that all partic-
ipants be screened, at a minimum, with a physical activity Evaluation of Student Work
readiness questionnaire or health history questionnaire. During the lesson, the instructor checks as students are
Special populations might require more extensive assess- completing the worksheet to ensure everyone has the correct
ment before participation. calculations before moving to the next. Further evaluations
and assessments are performed using case studies and sub-
RESULTS sequent laboratory activities and practicals. During these
evaluations, students are asked to do the following:
Expected Results • Answer how fat mass is lost to when someone loses
weight through exercise.
Part 1: prelaboratory.
• Calculate the expected weight loss for a client/patient
Students often struggle initially to answer the question,
when provided with their aerobic exercise routine.
“When you lose weight, where does it go? Literally, where is
• Mathematically prove to a client/patient that significant
the mass that was lost?” Most students indicate that it was
weight loss through exercise alone in only a few weeks is
“burned off” or “given off as heat” with others indicating
unrealistic for all but the very fittest individuals.
that it was “sweat out,” “as urine” or sometimes even “in the
• Using the metabolic equations, suggest appropriate in-
feces.” These common misconceptions can be refuted gently
tensity activities (e.g., walking/running paces) for cli-
in ways that students quickly and easily understand while
ents/patients with known fitness (V_ O2max).
also guiding them to the correct answer. If, for example, the
• Determine the pace at which someone can expect to run
instructor states while holding the bag of gummy bears, “I
an endurance race given his or her fitness level.
weigh 70 kg, if I eat 0.5 kg of gummy bears, how much will I
Student understanding of how fat mass is lost is improved
weigh?” Students understand this. “If the gummy bear mole-
due to this activity. In four semesters of assessment (120 stu-
cules are stored in my body for fuel and I later ‘burn’ them
dents), before the laboratory, 90% of students can correctly answer on end of semester
almost rhetorically, ask, “if you heat something up, is it then
exams. Student course evaluation data from these 4 semesters
heavier because it gained heat?” Similar questions can be
indicate that this laboratory activity was one of the most
asked to guide students to understand that simply losing
memorable for many students with >50% of students listing
water in sweat or urine is not sufficient to remove mass from
it as one of the top 3 of 10 laboratories from the semester.
the body that was stored as fat, because that would not
account for the carbon molecules and water is usually
Inquiry Applications
replaced. Within a few minutes, most students come to the
realization that most of the mass lost was exhaled as carbon A strength of this lesson is that it can be adapted to nearly
dioxide. any group interested in health and fitness. The concepts can
Advances in Physiology Education doi:10.1152/advan.00006.2021 http://advan.physiology.org 605
Downloaded from journals.physiology.org/journal/advances (046.004.080.155) on October 13, 2021.UNDERSTANDING EXERCISE WEIGHT LOSS WITH METABOLIC EQUATIONS
be simplified such that even those without a background in AUTHOR CONTRIBUTIONS
chemistry, physics, or physiology can understand the pre-
E.K.M. conceived and designed research; E.K.M. performed
mise and recognize the importance of the overall message. experiments; E.K.M. prepared figures; E.K.M. drafted manuscript;
Conversely, for more advanced students, expansion of the E.K.M. edited and revised manuscript; E.K.M. approved final ver-
biochemical and physiologic principles underscores the sion of manuscript.
complexity of the systems at work and can be discussed in-
depth. As with many complex scientific concepts, several REFERENCES
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