How did the actual exercise VO2 compare to the subject’s estimated VO2?

LABORATORY FIVE

Oxygen Deficit and the EPOC

Objectives:

1. To learn the causes of oxygen deficit and the EPOC.

2. To learn how to plot oxygen deficit and the EPOC from metabolic data.

3. To learn about energy pathways contributing to the oxygen deficit and the EPOC.

4. To learn about the basics of cycle ergometry.

Equipment Needed: 3 metabolic carts and connection materials, breathing masks and valves, 3 cycle ergometers, 3 metronomes, 3 stopwatches, 3 Polar heart rate monitors, Physician’s scale, stadiometer

When transitioning from a state of rest to exercise, the body’s demand for oxygen immediately increases. However, our bodies do not automatically increase our metabolism to the level required to sustain exercise. Anaerobic pathways must produce the required ATP until oxygen consumption increases enough for aerobic metabolism. The oxygen deficit refers to this initial delay in oxygen consumption at the start of exercise. After exercise termination during recovery, the body’s requirement for oxygen slowly returns to resting levels. As one’s metabolic rate remains elevated for a period after exercise is terminated, the oxygen “debt” must be repaid during a period called the EPOC (excess post-exercise oxygen consumption).

One measurement device for these metabolic parameters is the exercise cycle ergometer. The Monark (brand name) cycle ergometer has been the “gold standard” of testing devices since the late 1950’s in clinical laboratory settings. The Monark cycle is unique, as it is designed to measure actual units of work in a very precise fashion. This is a “mechanically-braked” stationary cycle with a friction belt that allows varying workloads to be set with a rotating handle. The pedaling resistance depends upon how much pressure is applied to the flywheel belt.

Ergometry is broken down into the words “ergo” meaning work and “meter” meaning measurement. Thus, ergometry is the study of measuring work. To understand how the Monark cycle ergometer calculates total work and energy expenditure, one should be familiar with the following units of measure:

• 1 kilopond-meter = work in which the product of force (kp) acts against a kg mass through a distance = 1 kp-m = 9.81 joules = 0.00234 kilocalories (kcal)
• 1 kilogram-meter = work in which the product of force (kg) acts against a kg weight through a distance = 1 kg-m = 1 kp-m (at sea level)
• 1 joule = 1 J = 1 Newton-meter = 0.101 kp-m = 0.000238 kcal = 1 watt-second
• 1 kilocalorie = 1 kcal = 426.85 kg-m = 4186 joules
• 1 kilogram = 9.8 newtons (N)
• 1 watt = 6.12 kg-m/minute = 1 Joule/second
• Work rate = Power = Work over some unit of time (e.g., kg-m/minute)

WORK (W) = FORCE (F) x DISTANCE (D) and POWER (P) = WORK (W)/ TIME (T)

Example: Batman lifts a 50 kg weight to a height of 2 meters in 30 seconds. How much work has he performed? How much power?

a) W = F x D b) W = 50 kg x 2 m c) W = 100 kg-m d) P = 100 kg-m/ 0.5 min. e) P = 200 kg-m/min

When applied to a cycle ergometer, we can determine the amount of work performed as well:

WORK (kg/m or kp/m) =
FORCE (cycle braking resistance in kilograms or Newtons) x
DISTANCE (distance in meters traveled by the flywheel rim per revolution)

Example: Keeley wants to pedal her Monark cycle with a resistance of 2 kp for 5 minutes. What is her average work rate (power) for that time period?

1. Work = Force (2 kg) x Distance (distance in meters traveled by flywheel rim/revolution)

2. Work = 2 kg x Distance

3. Distance = 1.62 meters (the circumference of the Monark cycle flywheel rim) x 3.75 (the # of revolutions the flywheel makes per 1 revolution of bike pedaling) x 250 revolutions (the total amount of revolutions for 5 minutes against a fixed resistance at 50 rpm)

4. Work = 2 kg x (1.62 meters x 3.75) x 250 rpm = Z kg-m for 5 minutes

5. Work (Z) = 2 kg x (6.075 meters) x 250 rpm = 3037.5 kg-m for 5 minutes

6. Work Rate (Power) = 3037.5 kg-m per 5 minutes of pedaling

7. Work Rate (Power) = 3037.5 kg-m / 5 minutes = 607.5 kg-m/minute

8. Work Rate (Power) ~ 600 kg-m/min (it is difficult to set a bike tension to 607 kgm/min)

9. Work Rate (Watts) ~ 607.5 kg-m/min / 6.12 = 99.26 ~ 100 Watts

Thus, Keeley’s average work rate is approximately 600 kg-m/min or 100 Watts

We can also estimate one’s oxygen consumption from cycle workloads, as you will see in this lab. This is performed by using the ACSM metabolic equation conversions found in the current edition of your ACSM Guidelines book. You will have the opportunity to do this as part of your data presentation on your graph. In the next semester, we will discuss more about cycle ergometry and the ACSM metabolic equations in greater detail, as there are many of these equations in the problems on the certification exams that you may take in the future.

It is important to calibrate the Monark cycle ergometer prior to any experimental exercise bout to assure that the subject is pedaling at an accurate workload. This is performed by hanging a “known weight” (usually 2-4 kg) from the suspension hook at the front of the flywheel. The kg weight will move the “pendulum” to the proper marker on the scale at the side of the cycle ergometer. The cycle can be adjusted if this marker is off. Cycle calibration will be performed to assure that the subject is pedaling at the proper set workload.

LABORATORY PROCEDURES

1. You will divide into 2-3 groups.

2. The data from your subject will be the data that you will use to write up your laboratory report.

3. Each student will have a role as presented below:

• 1 subject (will attach the Polar HR monitor strap tightly)
• 1 person to measure the height/weight of the subject and collect demographic data to be entered into the metabolic cart computer before the test
• 1 timer (handles the stopwatch)
• 2 metabolic cart operators at each cart (with lab instructor/teaching assistant)
• 1 cycle ergometer workload and seat height adjuster—assures that the cycle seat is the correct height for the subject and that he/she is pedaling the cycle ergometer at the proper workload by constantly watching the kg resistance throughout the experiment (adjusts workload when needed)
• 1 metronome operator—assures that the subject maintains the proper pedaling cadence throughout testing at 50 rpm (very important role)
• 1 student to help the subject attach the facemask, headgear and breathing tube—this student will also be the assistant to the subject for motivation and will clean the cycle after the test has been completed
• 2 “cleaner-uppers” who will remove the mask after the test, dissemble all parts, and clean the parts in accordance with the instructions

4. It is important that the subject warm-up prior to cycling.

5. The metabolic cart operators will calibrate the metabolic cart prior to the test with the help of the lab instructor/TA by reading through the calibration procedures.

6. The subject should first be weighed (without shoes) with weight calculated in kilograms (convert from lbs. for your lab write-up) and height measured in inches.

7. The subject will then prepare for metabolic analysis:
a. The subject will attach the Polar strap. The metabolic cart will pick up the HR. It is important that the subject be close to the cart in order for the HR to be recorded properly.
b. One student will help the subject attach the facemask and headgear and hook up
the subject to the breathing tube connected to the metabolic cart.
c. The metabolic cart operators and instructor will assure that all systems are
working and that the subject’s ventilation is being measured properly.

8. The metronome should be set at 50 beats/min for the cycle ergometer test.

DATA COLLECTION

1. The subject will sit quietly in a chair for 5 minutes while resting metabolic gases
are collected. The subject should be familiar with cycling and should be able to push a
workload of 2 kg on the Monark cycle for at least 10 minutes.

2. The subject will then mount the cycle after the appropriate seat height has been
determined and will start pedaling at 50 rpm with a set resistance of 2 kg.

3. The subject’s VO2 will be measured/recorded every minute for this experiment.

4. The subject will pedal for 10 minutes at 50 rpm at 2 kg (100 watts or 600 kg/m/min) on
the ergometer after the 5-minute resting period.

5. After 10 minutes of exercise, the subject will stop pedaling.

6. The subject will then relax as their VO2 is measured for another 10 minutes in a chair
during resting recovery.

7. The subject will then be disconnected from the cart, the mouthpiece dissembled and
cleaned (per instructions by the sink), and the breathing tube washed out and hung up.

8. The data will be put on moodle for all group members to access.

LABORATORY FIVE DATA PRESENTATION

1. Type an abstract summarizing this laboratory exercise using the Adobe Reader Lab Report file. You are limited to 2550 characters (about 425 words).

2. Calculate the estimated VO2 for the workload pedaled on the cycle ergometer for your subject:
a. Determine the work rate (see example below for a 1 kg cycle resistance)
b. Divide this number (kgm/min) by body mass (kg)
c. Multiply this number by 1.8 to convert to the total O2 cost to ml/kg/min.
d. Add 7.0 ml/kg/min to this number, which represents the “resting” and “unloaded
cycling” component of the cycle ergometer equation (also see ACSM Guidelines book).
e. This value represents the estimated relative VO2 for the workload (ml/kg/min) based
upon the ACSM metabolic equations.

Example:
 VO2 (mL • kg-1• min-1) = 1.8 (work rate / body mass)
+ 3.5 mL•kg-1 • min-1 + 3.5 mL•kg-1 • min-1
(resting VO2) (unloaded cycling VO2)
 Work rate (WR) = 1.0 kg x 6 m x 50 rpm
 WR = 300 kg • m • min-1

Please show all your calculations for your subject.

3. Plot the estimated VO2 and actual VO2 to help calculate the Oxygen Deficit and EPOC:

a. Using graph paper (or a computer-generated graph), plot the x-axis as time
(minutes with 1-minute hash marks) and the y-axis as VO2 (ml/kg/min).
Below “time” on the X-axis, label “REST”, “EXERCISE”, and “RECOVERY”. Be sure
to label your graph properly.

b. Plot the measured VO2 data points for every minute of data collected: 0-5
minutes = Rest; 5-15 minutes = Exercise; 15-25 minutes = Recovery.
Total number of units on the X-axis: 0-25 minutes

c. Be sure that your graph is laid out in “landscape” format and covers the entire
page. This is critical to truly visualize the oxygen deficit and the EPOC.

d. Be sure to color-code and symbol-code all of the lines on your graph.

e. Connect all of the subject’s VO2 data points with one continuous line.

f. After you determine the value of the estimated VO2 for your subject, draw a
straight line across the entire top of the graph where the estimated workload VO2 (ml/kg/min) lies. Color- and symbol-code this line.

g. Draw a solid line across the graph representing a line of best fit of the resting
VO2 data (5 minutes). This line should best bisect the 5 data points at rest. Do
not take an average of the 5 points and plot a line—“eyeball” the 5 data points
and draw a straight line that you feel best bisects all the data points most
effectively. This line should lie fairly close to the X-axis (be sure to color- and
symbol-code all lines). This line should also run above the entire X-axis.

h. Do the same for the exercise VO2 values (10 minutes) from your plotted
exercise data points and draw a single, straight line of best fit across the top of
the graph representing the best representation of the exercise VO2 data points.
Color- and symbol-code this line.

i. Do the same for the recovery VO2 values (10 minutes) from your plotted
data points and draw a single line above the X-axis representing the line of
best fit of the recovery VO2 data. NOTE: The resting and recovery VO2
lines of best fit could be connected and may be about the same, as the average
VO2 values at rest and recovery may be very similar depending upon the subject.

j. If you have any “outlier” data (data points that don’t make sense) exclude these.
Simply circle these data points and label as “outliers”—do not include these data
points in your lines of best fit.

k. Using the Oxygen Deficit/EPOC slides from your lab presentation as a model (or
from your textbooks), plot the O2 deficit and the EPOC. Shade in these areas on your graph as two different colors. Be sure to use the actual VO2 line of best fit instead of the estimated VO2 line of best fit for your O2 deficit and the EPOC plotting.

LABORATORY FIVE QUESTIONS

1. Locate an article from a non peer-reviewed source (internet, magazine, etc) that talks about the EPOC in response to a specific type of exercise as a major contributor to weight loss. Then find 2 peer-reviewed sources that investigate the caloric expenditure during EPOC in response to similar exercise and discuss, using physiological justification, whether the peer-reviewed sources support or refute the article. You must cite you work, include a bibliography, include the abstracts of your peer reviewed sources, and include a copy of the non peer reviewed article.

2. How did the actual exercise VO2 compare to the subject’s estimated VO2? What does this indicate about your subject’s cardiovascular fitness level? What were possible reasons for this (e.g., including sources of measurement error)?

3. Tony Stark is pedaling a Monark cycle ergometer with a 3 kg resistance at 50 rpm for 1 minute. What is his work rate (power) in: a) kg-m/minute, and b) Watts? Please show all math (including what his actual work is with dimensions of the Monark cycle flywheel rim) using the example in your lab packet. Be sure to include proper units of measure, unit cancellations, and all mathematical work.

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