University of Northern Iowa



PEMES 3153 Physiology of Exercise

Understanding VO2 and Power Units

Before coming to lab, read and understand pages 120-123 in your text.

The purpose of this lab is to become familiar with the different units used to quantify both oxygen consumption (VO2) and power.

VO2 Units

VO2 is expressed in absolute units and in relative units. The absolute units are a volume per minute and are either milliliters per minute (ml.min-1) or liters per minute (l.min-1). The absolute units express the oxygen consumption as a total quantity for the entire body mass. In contrast the relative units are a volume per kg of body mass per minute (ml.kg-1.min-1). The relative units are identifying how much oxygen is being consumed for every one kg of body mass. That is why the volume of oxygen is so much less in relative units than in absolute units.

Converting between the two sets of units for VO2 is very simple and makes sense if you remember what each set of units is expressing. To convert from the absolute set to the relative set you just divide the absolute units in ml.min-1 by the body mass in kg. To covert from the relative set to the absolute set you just multiply the relative set by the body mass in kg.

To help you understand when each set of units should be used we will compare VO2 units between two modes of exercise, walking and biking.

Instructions: You MUST collect the data indicated below before you come to lab. You MUST also do it in the order indicated (bike first, then the treadmill).

1. Using an upright electronic LifeFitness bicycle (not recumbent) ride at the level 10 intensity (100 watts) for 5 minutes maintaining 60-90 rpms. Adjust the seat height so that when you pedal you almost fully extend your lower leg at the knee. There should be no more than a 15-20 degree bend at the knee when you are in the down position of the pedal stroke. Make sure the monitor displays the Constant Cal/Hr Mode. This is located on the right side of the bike’s digital panel just to the right of where the numbers are located (See the S label on the diagram). After riding for 5 minutes at the level 10 intensity, grab the metal plates on the handlebars to measure your heart rate. Record your heart rate.

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2. Using one of the treadmills upstairs in the WRC Fitness area, walk on the treadmill at as fast a walking pace as you can maintain for 1 mile. About 20 seconds before the end of the mile, grab the metal plates on the handlebars and measure heart rate and note the time it took to walk the mile. Record both the heart rate and the time it took to walk the mile.

3. Steady-state HR. Using one of the treadmills upstairs in the WRC Fitness area, run on the treadmill at 6 mph for 5 minutes. During the first minute of the run, grab the metal plates on the handlebars to make sure you can get a heart rate. Once you have confirmed you can get your heart rate, continue running at 6 mph until you complete the 5 minutes. At the end of 5 minutes and while still running, grab the metal plates on the handlebars and measure heart rate. Stop the treadmill and record your heart rate.

Bring your data to lab

1. Using Excel, create a spreadsheet and record the data for each student using the format below.

|Subject |Age |

Biking VO2 in ml.kg-1.min-1 = [(watts/mass) x 10.8] + 7.0 where mass = weight in kg

Construct a table to display the following average variables for males and females: steady-state VO2 while running and biking in absolute units and in relative units; average heart rates while running and biking; and VO2max in relative and absolute units. Based on the data, answer the following:

1. It would be expected that on average the males would have a higher VO2max in both relative and absolute units than females. Was this the case? Provide a physiological rationale for why males would be expected to have a higher VO2max.

2. Compare and contrast the steady-state VO2 for the males and females for running at 6 mph. You would expect similar values for males and females when expressed in relative units but you would expect males to have higher values when expressed in absolute units. Does your data support this? Provide a physiological rationale which explains this expectation.

3. Compare and contrast the steady-state VO2 for the males and females for biking at 100 watts. You would expect similar values for males and females when expressed in absolute units but you would expect males to have lower values when expressed in relative units. Does your data support this? Provide a physiological rationale which explains this expectation.

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