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.

Class activity

measuring VO₂max (VO₂peak)

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 participant to have their VO₂ measured, plus one student for each of these tasks: time master, RPE collector, HR collector, computer watcher, TM speed adjustor, TM incline adjustor, and recorder

Instructions:

One subject will walk/run on a treadmill until voluntary exhaustion. There are many protocols that can be used; please follow the instructions from your course instructors of which test will be used.

During the test, the participant will be monitored with a HR monitor and metabolic cart. There are sevenother students who will assist with data collection. RPE should be collected at 30 seconds remaining in the stage, and HR with 15 seconds remaining.

Please be sure you copy down the data from the test so that you can practice the calculations and graphs that you will need to do for the lab report.

After the test, you will use the collected variables to practice calculating VO₂ by hand. The point of this calculation practice is to help students 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.

This lab has an accompanying handout to help you collect data from the lab. It is provided as a Word document so you can use it either electronically or print it out to use.

Calculations

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

[latex]VO_{2} =  VIO_{2} – VEO_{2} =(VI \times FIO_{2}) – (VE \times FEO_{2})[/latex]

[latex]FIO_{2}\  =\ \ 0.2093\ \ \ \ \   FEO_{2}[/latex] can be measured

VI or VE (only one) 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.

[latex]VI \times FIN_{2} =VE \times FEN_{2}[/latex]

[latex]FIN_{2} =\ \ 0.7904[/latex]

[latex]FEN_{2}\ =  [1 – (FEO_{2 }+ FECO_{2})][/latex]

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

Therefore:

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

Or:

[latex]VE  = \frac{VI \times 0.7904}{(1 – (FEO_{2} + FECO_{2}))}[/latex]

*To calculate VO₂ if VE is measured:

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

*To calculate VO₂ if VI is measured:

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

CALCULATING CARBON DIOXIDE CONSUMPTION

[latex]VCO_{2}\  =\  (VI \times FICO_{2}) – (VE \times FECO_{2})[/latex]

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:

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

*If VE is measured:

[latex]VCO_{2}  =  VE \times FECO_{2}[/latex]

Other useful equations:

[latex]RER = \frac{VCO_{2}}{VO_{2}}[/latex]

Helpful table of gases

A table with inspired and expired gases
(Note: Pressbooks cannot do subscript in a table)