Lab 4 - Maximal Oxygen Consumption
PEMES 3153 Physiology of Exercise
Introduction
One characteristic of living animals is that they all give off heat. As a result of
cellular respiration and cellular work, heat is produced. An operational definition of
metabolism is the rate of heat production which describes the metabolic rate.
respiration
work
foodstuffs + O2
heat + ATP
heat
The direct measure of heat production, called direct calorimetry, is a technically
difficult problem so an alternative method is to measure the volume of oxygen consumed
or utilized by the body for ATP production. The determination of the metabolic rate from
the measure of oxygen consumption is called indirect calorimetry.
In our laboratory, we utilize a metabolic measurement cart for our indirect
calorimetry measurements. This system measures the total volume of ventilated air as
well as the differences of oxygen and carbon dioxide levels from the ambient and expired
air. The system’s computer uses this information to calculate the volume of oxygen
utilization (VO2) and carbon dioxide production (VCO2). To take these measurements, a
subject is fitted with a low-resistant, two-way non-rebreathing valve in her/his mouth
which directs all expired air to the metabolic measurement cart via a long flexible hose.
As the expiratory air enters the cart, it passes through an instrument which measures air
volume. The air enters a mixing chamber from which a small sampling line draws air
from the mixing chamber to an oxygen and a carbon dioxide analyzer which are
interfaced, along with the air-flow meter, to a computer which makes the necessary
computations.
Schematic of a Metabolic Measurement Cart
subject
expired air
volume analyzer
O2 analyzer
mixing
chamber
CO2 analyzer
computer
The measurement of maximal oxygen consumption (VO2max or MaxVO2) has
long been used to evaluate aerobic fitness. In performance, this measure is strongly
related to endurance activities of short duration (one mile run) and moderately related to
longer endurance (10K run and longer) tasks. In health, this measure has been linked to
cardiorespiratory function as well as skeletal muscle oxygen consumption capabilities.
Thus it has been viewed as the measure that reflects cardiorespiratory endurance, one of
the health-related fitness components.
Directly measuring VO2max requires laboratory instrumentation (metabolic cart),
a mode of exercise that utilizes a lot of muscle (running for instance), an appropriate test
protocol that minimizes oxygen deficit, and a motivated subject to perform a continuous
test until exhaustion. While this is possible in an Exercise Physiology Laboratory, it is
less practical in most wellness centers, sports medicine rehabilitative centers, and
schools. Therefore many times tests are used to indirectly evaluate VO2max based upon
performance to maximal efforts (time to fatigue on a progressive treadmill test), time in
an aerobic task (1.5 mile test), or using the submaximal response to exercise and
estimating the VO2max (heart rate response during a walking test).
The purpose of this laboratory is to demonstrate a VO2max test using a direct
measurement and learn the criteria for assessing whether a "true" VO2max value was
obtained. Differences in VO2max between males and females will also be evaluated.
Measurements
1. Two volunteer subjects, one male and one female will be solicited. Each will be
subjected to a protocol using the treadmill and metabolic cart to measure the highest
rate of oxygen consumption (VO2). A Polar heart rate transmitter will be used to
monitor heart rate during the test.
2. For this laboratory experience, a protocol that starts with a warm-up of 3.5 mph for
two minutes, 5.5 mph for two minutes, and increases the speed 0.5 mph every one
minute until a running velocity comfortable for the subject is reached. Then the grade
will be increased 1% every minute until reaching volitional exhaustion. It is important
in this type of maximal effort to provide verbal encouragement for the subject to
motivate him/her during the latter stages of the test.
3. The following variables will be determined each minute of the test: VO2 in ml.kg1.
min-1, VO2 in ml.min-1, VE in L.min-1 , RER, and heart rate.
Analysis
1. Using the article provided (“Criteria for VO2 max” on the website), determine if each
subject reached a true VO2max and identify the criteria you used to make that
decision.
2. Normally you expect and average male to have a higher VO2max than an average
female of the same age and training level. What are three reasons the average male
has a higher VO2max than the average female?
3. If all you knew was the data collected on each subject and that the subjects were
equally trained in running and cycling and were the same age, which subject would
do better in a 5 mile running race on a track? Which would do better on a 10 mile
bicycle race over flat terrain? Explain your answers using physiological principles
and rationale.