Exercise Metabolism
Diagrams, Definitions and Key Points
Estimated Time: Class time and about 45 minutes after class.
Note: Follow along with the class discussion as you start this worksheet in class. We will not wait for
you to draw all the graphs; therefore, you should use the Exercise Metabolism PowerPoint in
combination with the section in your text that discusses these concepts to finish this worksheet outside
of class.
Worksheet Outcomes:
1. Students will understand the relationship between oxygen consumed and carbon dioxide
produced.
2. Students will explain the factors that contribute to excess post-exercise oxygen consumption
(EPOC).
3. Students will explain why oxygen consumption increases during long-duration exercise even
when work output is not increasing.
4. Students will define the “lactate threshold”.
5. Students will write the formula for respiratory exchange ratio (RER)
6. Students will begin memorizing key values of RER that indicate relative percentages of
carbohydrate and fat that are being used for energy at given intensities.
7. Students will explain how the bicarbonate buffering system increases RER to values above 1.0.
8. Students will graph the relationship between carb and fat utilization as exercise intensity
increases.
9. Students will graph the relationship between carb and fat utilization as a function of exercise
duration.
10. Students will graph the time-course of carb and fat utilization based on where they are located
(i.e. plasma sources or intramuscular sources) as exercise progresses.
11. Students will graph the carb and fat utilization based on where they are located (i.e. plasma
sources or intramuscular sources) as exercise intensity progresses.
12. Students will write a statement about how substrate (carb or fat) utilization is based on both
exercise intensity and duration.
Task: Answer the following questions and graph the respective relationships.
1. Write a working definition for VO2 using words a 12-year-old person could understand.
2. Explain what is meant by a “MET”.
3. Calculate the amount of oxygen you consume (in Liters) in 24 hours—you will need the
following:
a. Your weight in kilograms. To get this, take your body weight in pounds and divide it by
2.2. ___________ (weight in pounds) divided by 2.2 = _____________ (wt in kg)
b. The conversion from milliliters to liters: milliliters divided by 1,000 = Liters.
4. Calculate the number of calories you would expend at total rest for 24 hours. To get this, take
your liters and multiply it by 5.
VO2
5. Graph oxygen consumption below. Include the oxygen deficit portion as well as the postexercise oxygen consumption (EPOC). Draw the line for EPOC in such a way as to make it easy to
identify the fast and slow components and label them.
Time
6. Summarize what is happening in the fast and slow portions of EPOC, respectively (i.e. what is
being replenished and what things are elevated in the body).
7. Explain in the graph above how the relative sizes of oxygen deficit and EPOC would change
based on whether the exercise session was more moderate intensity vs high intensity.
Given that higher intensity exercise utilizes more oxygen, the oxygen deficit would be
greater and thus the EPOC would be greater.
8. Given the relationship between oxygen consumption and caloric expenditure, which exercise
intensity would consume the most oxygen in the post-exercise period (and burn the most
calories), moderate intensity or high intensity?
High intensity
9. Explain what happens when we have an active recovery between interval sprints and why active
recovery is preferred to total rest. (Hint: It has to do with pyruvate.)
10. List a few reasons why oxygen consumption (VO2) rises as exercise is prolonged even if we are
not increasing our exercise intensity (i.e., running/biking faster etc.).
Increased body temperature and hormones increase your need for oxygen. Body temp goes up with
longer exercise time.
11. Write a working definition for VO2 max using words a 12-year-old person could understand.
The most amount of oxygen your muscles can use no matter how much harder you try to work.
12. Explain in words a 12-year-old could understand, explain what is meant by the lactate threshold.
13. If you were running, and you were not able to directly measure your lactate levels, how could
you tell about where your lactate threshold was? (Hint: It would be related to your ability to
increase and maintain your pace.)
It usually takes place at about 50-60% of your VO2 max, or 65-80% if you are a trained individual.
14. Traditionally, lactate threshold was called “anaerobic threshold”. List the four reasons why the
term anaerobic threshold is not the best term.
Anaerobic implies there is no more oxygen available, but that’s not always true. Maybe the “hydrogen
shuttle” can’t keep up. FT fibers tend to convert pyruvic acid to lactic acid. Maybe decreased removal by
tissues.
15. Some people say muscle soreness is due to “lactic acid”. Explain why this is probably not true.
16. Write the formula for Respiratory Exchange Ratio (RER).
17. Complete the following table and begin memorizing the carb and fat percentages associated
with RER values of .7, .85, and 1.0. (Hint: % fat + % carb must equal 100.)
RER
0.70
0.75
0.80
0.85
0.90
0.95
1.00
% Fat
100
83
67
50
33
17
0
% Carb
0
17
33
50
67
83
100
Kcal (Liters/min)
4.69
4.74
4.80
4.86
4.92
4.99
5.05
18. Review the kcal column on the table above. Why is 5 kcal per liter of oxygen consumed a good
estimate? (Keep the answer simple—this question is only there to draw your attention to this.)
19. Write the equation for the “bicarbonate buffering” system. You will need the following in your
equation: H2CO3, CO2, H+, HCO3-, H2O, CO2.
H+ + HCO3- ->
20. Explain why RER might go above 1.0. In other words, why might we produce more CO2 than O2
that we consumed? (Hint: Review the bicarbonate buffering system equation above.)
% of energy from fat and
carbohydrates
21. Complete the graph below of the relationship between exercise intensity and the percentage of
fat and carbohydrate used as a fuel source. On your graph, write the exercise intensity at which
the fuel source crosses over from fat to carbohydrate.
% VO2 max
22. Explain the reasons why we increase the use of carbohydrate as a fuel source as exercise
intensity increases.
The faster you move, the more fast twitch fibers you recruit because they have more mitochondria’s. As
the temperature of your body goes up, the more blood epinephrine you release, and thus more
glycogen breakdown.
% of energy from fat and
carbohydrates
23. Complete the graph below of the relationship between exercise duration and the percentage of
fat and carbohydrate used as a fuel source. On your graph, write the exercise intensity at which
the fuel source crosses over from fat to carbohydrate.
Exercise time (duration)
24. Explain the reasons why we increase the use of fat as a fuel source as exercise duration
increases.
% of energy expenditure
25. Complete the graph below of the percentage of energy derived from the four major fuel sources
(muscle triglycerides, plasma FFA, blood glucose, and muscle glycogen) during prolonged
submaximal exercise. It is not important that you know the exact percentages and exact times if
you understand the trends.
Exercise Time (Duration)
% of total fuel source
26. Use the graph on the Exercise Metabolism PowerPoint to complete the graph below of the
percentage of energy derived from the four major fuel sources (muscle triglycerides, plasma
FFA, blood glucose, and muscle glycogen) at different exercise intensities. Label the y-axis in
20% increments. Label the x-axis with the following percentages: 25, 65, and 85 and make the
respective bars above those columns as illustrated on the graph on the PowerPoint. It is not
important that you know the exact percentages of substrates used at given intensities if you
understand the trends.
Exercise Intensity (% VO2 max)
27. Make a general statement about the role of exercise duration on how the body uses fuel
sources. Explain both the trends for use as well as the sources of carbs and fats used as exercise
goes on. This will probably take three or four sentences.
28. Make a general statement about the role of exercise intensity on how the body uses fuel
sources. Explain both the trends for use as well as the sources of carbs and fats used as exercise
goes on. This will probably take three or four sentences.