9 Chapter 9: Measuring VO2peak

Melissa Markofski

Background

Aerobic metabolism utilizes oxygen in the degradation of carbohydrates and fats; therefore, oxygen consumption (VO2) can be considered a measure of aerobic metabolism. Aerobic (cardiorespiratory) fitness can be measured when the participant gradually exercises toward maximal effort (VO2max). It reflects the body’s ability to extract and use oxygen at the cellular level as well as the ability of the cardiovascular and respiratory systems to transport this oxygen to the cell.

During exercise there are differing amounts of aerobic and anaerobic metabolism occurring depending primarily on the intensity and duration of the activity. Measurement of carbon dioxide production (VCO2) and calculations of the respiratory quotient or respiratory exchange ratio (RER) helps determine the aerobic and anaerobic contributions towards the energy expenditure of the activity.

 

You may find it helpful to think about the Fick equation:  VO2= Q * a-vO2diff    And cardiac output: Q = SV * HR

 

Class activity

Activity 1: measuring VO2max (VO2peak)

PRE-EXERCISE INSTRUCTIONS: It is recommended not to eat for at least 2 hours before the test, no heavy meals for at least 4 hours before the test, and hydrate (0.5-1.0L of water 2-4 hours before the test).

 

Equipment: motor-driven treadmill, gas analyzers and computer (commonly referred to as “metabolic cart”, because on the cart is all the equipment needed)

Participants: One person is the participant and has their VO2 measured. During a test, the test administrators monitor the time duration, participant’s RPE, participant’s HR, adjust the treadmill speed, and record all measures during the test. (in a non-classroom setting the test moderators perform multiple tasks during the test)

Instructions:

One participant will walk/run on a treadmill until voluntary exhaustion. There are many protocols that can be used , however a discontinuous exercise protocol is commonly used for this test. A common set-up includes multiple stages of 3 minutes with each stage increasing in intensity (treadmill speed and/or grade) until the subject reaches exhaustion.

*Note: this test can also be performed using a cycle ergometer, in this case the resistance and RPM would change with every stage.

Safety first! The participant will use hand signals to communicate during the test. Pay attention to why they are communicating, and also look out for potential problems. For example, are they creeping too far towards the back of the treadmill?

 

During the test, the participant will be monitored with a HR monitor and metabolic cart. RPE should be collected at 30 seconds remaining in the stage, and HR with 15 seconds remaining.

For this lab, you will use the example collected variables to practice calculating VO2 by hand. The point of this calculation practice is to help you understand where the values “come from” i.e. what variables change and how this impacts VO2. Check your calculated values against what the computer calculated, as the values should be very similar.

There is also an accompanying handout of what the data collection sheet during this test would look like if we were collecting data in person.

Video #1: Example of a VO2max test

Video #2: VO2 max test explained- with Lindsey Vonn

 

Calculations

F = fraction; V = volume; I = inspired; E = expired

VO_{2} =  VIO_{2} - VEO_{2} =(VI \times FIO_{2}) - (VE \times FEO_{2})

FIO_{2}\  =\ \ 0.2093\ \ \ \ \   FEO_{2} can be measured

 

VI or VE can be measured by the metabolic cart. Whichever one is not measured has to be calculated.

 

The amount of N2 inspired is equal to the amount of N2 expired.  This allows us to calculate VI if VE is measured, or VE if VI is measured.

 

VI \times FIN_{2} =VE \times FEN_{2}

FIN_{2} =\ \ 0.7904

FEN_{2}\ =  [1 - (FEO_{2 }+ FECO_{2})]

 

After substituting: \ \ VI \times 0.7904\  =\  VE \times [1 - (FEO_{2} + FECO_{2})]

 

Therefore:

VI = \frac{VE \times [1 - (FEO­{2} + FECO­{2})]}{0.7904}

Or:

VE  = \frac{VI \times 0.7904}{(1 - (FEO_{2} + FECO_{2}))}

 

 

*To calculate VO2 if VE is measured:

[ VO_{2}=VE  \times \{ [ ( \frac{( 1 - ( FEO_{2}+ FECO_{2}))}{0.7904})  \times 0.2093] -FEO_{2} \}

 

*To calculate VO2 if VI is measured:

VO_{2} = VI \times \{0.2093 - [\frac{0.7904 \times FEO_2}{(1-(FEO2_2 + FECO_2))}]\}

 

 

CALCULATING CARBON DIOXIDE CONSUMPTION

 

VCO_{2}\  =\  (VI \times FICO_{2}) - (VE \times FECO_{2})

 

Since the CO2 in inspired air is 0.03%, it can be considered negligible (or zero), so the first part of the equation drops out. Therefore, to calculate VCO2:

 

*If VI is measured:

VCO_{2}= \{ \frac{VI  \times 0.7904}{[ 1- (FEO_{2} + FECO_{2})]} \}   \times FECO_{2}

 

*If VE is measured:

VCO_{2}  =  VE \times FECO_{2}

 

In the inspired gas: In the expired gas:
FIN2 = 0.7904 FEN2 = [1-(FEO2 + FECO2)]
FIO2 = 0.2093 FEO2 = measure
FICO2 = 0.0003 FECO2 = measure

 

Virtual Lab Activity
Learn how to conduct a VO2max test:
1. Watch Video #1 and Video #2
Practice Calculation:
You conduct a VO2max test on a 28 year old male who weighs 90.9kg. His VE=95.55 L/min, FEO2=17.23%, and FECO2=3.59%
1. What is his absolute VO2max?
2. What is his relative VO2max?
2. What is his cardiorespiratory fitness classification? (Textbook Table 3.2)