Work Physiology Laboratory
VO2max
Test - Summary of Results
What is Exercise Physiology?
Exercise physiology is a scientific discipline
that focuses on how an organism responds to exercise. Exercise represents one of the greatest
stresses that an organism can encounter.
Therefore exercise represents an outstanding model for studying human
and animal physiology. Most people are
familiar with the study of exercise physiology as it relates to sport performance. However, in the last several decades it has
become apparent that the study of exercise physiology is also relevant in
clinical settings. This realization has
emerged form our understanding of how exercise can be used in both the
treatment and prevention of multiple diseases including cardiovascular
diseases, pulmonary diseases, diabetes mellitus, and several types of cancers.
What physiological variables
influence athletic performance?
Stephen
Seiler, an exercise physiologist at the Institute of Health and Sport at Agder
College in Norway, has an interesting web site that discusses many topics
related to physiological limits to human exercise performance, click on this link
to check it out - http://home.hia.no/~stephens/exphys.htm. Multiple physiological variables
influence athletic performance. Among those variables that influence
endurance performance, the following variables are discussed on this page:
percent body fat, VO2max, the anaerobic threshold, running economy,
and anaerobic capacity. Several of these
variables can distinguish between highly trained and untrained subjects.
However, within the trained population there is considerable variability for
each. For example, highly trained athletes tend to have higher VO2max
values than untrained individuals. These
high VO2max values are partly responsible for the better endurance
performance of the highly trained runner.
The same can not be said about a group of highly trained athletes: the
person with the highest VO2max values are not necessarily the best
runners, nor visa versa. There are many
examples in the literature of outstanding athletes with modest VO2max
values or relatively untrained individuals with outstanding VO2max
values (likely due to genetic endowment). So, how can physiological
testing help athletes and coaches? [1]
%BF - Percent Body Fat
Success
at the highest levels of many sports requires a specific physique. Body
composition is one variable related to physique. A very basic assessment of body composition
allows for the division of the body components into fat tissue and lean
tissue. Percent Body fat (%BF) is the
proportion of one's body made that consists of fats. There are currently several methods for
assessing percent body fat. Most methods
for assessing percent body fat are based on the relationship between body density
and percent body fat. The gold standard
(best method) for assessing body density (and thus percent body fat) is by
densitometry, which has traditionally made use of underwater, or hydrostatic,
weighing. Measurement of skin-fold
thicknesses also allows for estimation of body density and percent body
fat. Measurements of %BF determined by
skin-folds usually correlate well with %BF determined by hydrostatic
weighing. It should be noted, however,
that there are several underlying assumptions made when using skin-fold
measurements to determine %BF. Average
percent body fat values for 20-29 year-old subjects in the general population
are 15.9% for men and 22.1% for women [2]. The percent
body fat among athletes of most, but not all, sports are typically lower than
those recorded in a general population.
For example, %BF values for competitive runners are typically between
4-10% in men and 7-15% in women [3]. OU X-C male. OU X-C female.
VO2 – Oxygen Consumption
Oxygen consumption is the amount of
oxygen taken up and utilized by the body.
The oxygen taken into the body at the level of the lungs is ultimately
used for the production of ATP in the mitochondria of our cells. Because most of the energy in the body is
produced aerobically, VO2 can be used to determine how much energy a subject is
expending. VO2 can be reported
in absolute terms (L/min) or relative to body mass (ml/kg*min). Oxygen consumption is dependent on the
ability of the heart to pump out blood, the ability of the tissues to extract
oxygen from the blood, the ability to ventilate and the ability of the alveoli
to extract oxygen from the air.
VO2 = HR x SV x A-vO2difference
Where:
HR = heart rate in beats per minute
SV = stroke volume (amount of blood pumped out of the
heart per beat)
A-vO2difference = the amount of O2 extracted from the blood by the
tissues
VO2 = VE x (.2093 – FEO2)
Where: VE =
amount of air moved in and out of the lungs/minute
(.2093 –
FEO2) = the amount of O2 extracted
from the air by the lungs
Resting absolute values tend to be around
.2-.5L/min in men and .15-.4L/min in women.
The approximate resting relative VO2 for all individuals is
3.5ml/kg*min. Oxygen consumption is most
frequently determined using open-circuit spirometry. Open circuit spirometry can be used not only
for the determination of oxygen consumption, but also for the determination of
metabolic rate (indirect calorimetry).
Click here to see the VO2
response to exercise.
VO2max
– Maximal Oxygen Consumption (Aerobic Capacity)
Maximal oxygen consumption is the
highest VO2 value recorded during maximal exercise. A number of objective criteria can be used
post-test to determine whether or not the peak VO2 value during the
test can truly be considered a maximal value.
VO2max is thought to be the best indicator of aerobic
capacity and therefore of aerobic fitness. It is also a relatively good predictor
of endurance performance (however it is not the only predictor of performance). VO2max tends to be higher in men
than in women. College age males have an
average VO2max of 45ml/kg*min and college age females have a VO2max
of about 35ml/kg*min. The highest
absolute VO2max values recorded have been in large endurance
athletes, such as elite heavyweight rowers (values of over 7L/min have been recorded),
whereas the highest relative VO2max values are typically recorded in
small endurance athletes such as cross-country skiers, cyclists, and distance
and middle distance runners (values of up to 90ml/kg*min have been
recorded). VO2max tests can
also be used clinically to assess the type and severity of cardiovascular or
pulmonary limitations to exercise. Check
out http://home.hia.no/~stephens/vo2max.htm
for more information about VO2max and aerobic capacity.
VO2max can increase with training. An untrained individual may be able to
increase VO2max by as much as 15-20%. However, in well trained athletes increases
in VO2max may not be as great (they are already nearly as high as
they can go). Fortunately for these athletes, with continued training they can
become more efficient (economical), such that they can go faster for a given
oxygen consumption. Additionally, the
percent of VO2max that the athlete can sustain for prolonged periods
of time is also very trainable. OU X-C male. OU X-C female.
VCO2 – Carbon Dioxide production
Carbon dioxide (CO2) is a
by-product of cellular metabolic processes.
Most of the CO2 given off by the body comes from this cellular
respiration. However, during high
intensity exercise some of the CO2 that the subject is blowing off
comes from buffering of the blood (in order to maintain proper pH). Click here to see the VCO2
response to exercise.
RER – Respiratory Exchange Ratio
This is the ratio of carbon dioxide
production to oxygen consumption (VCO2/VO2). At rest and during low intensity exercise the
RER reflects the type(s) of fuel substrates being used by the cells for the
production of ATP. For example, an RER
closer to 0.70 suggests that primarily fats are being used for the production
of energy, whereas an RER closer to 1.0 suggests that primarily carbohydrates
are being used. During high intensity
exercise some of the CO2 that the subject is blowing off comes from
buffering of the blood and thus no longer reflects solely cellular metabolic
events. The normal range for RER at rest
and during low intensity exercise is .7-1.0 but values may exceed 1.2 during
high intensity exercise. Click here
to see the RER response to exercise.
VE – Pulmonary Ventilation
Pulmonary ventilation is the amount of
air moved in and out of the lungs per minute.
It is dependent on the depth of each breath (the tidal volume) and the
number of breaths taken per minute (breathing frequency). At rest most individuals have a VE of
6-10L/min and maximal exercise values (VEmax) are in the range of 100-170 for
most individuals. In elite rowers values
of up to 250L/min have been recorded. VE
increases linearly with VO2 and workload until about 60% of
maximum. Beyond this point it increases
at a higher rate. Click here to see the VE response to
exercise. OU X-C male.
OU X-C female.
HR – Heart Rate
Heart rate (HR) is the number of times
per minute the heart beats. Cardiac
output, the amount of blood pumped out of the heart per minute, is dependent on
HR and stroke volume (SV, the amount of blood pumped out per beat. Resting HR
for most individuals is between 60-75 beats/minute. Resting HR tends to be lower in individuals
who exercise on a regular basis. Maximal
heart rate (HRmax) values are frequently estimated based on the subject’s
age according to the formula: HRmax = 220-age. It should be noted that this formula
provides only a very rough estimate of maximum heart rate.
FEO2 – Fraction of expired air that
is oxygen (O2%)
FEO2 is the percent of expired air that
is oxygen. The air we breathe in is
20.93% oxygen and we typically extract 3-6% of the air that is oxygen. Thus, the air that we exhale is usually
15-18% O2. Low values for FEO2 suggest
that the subject is extracting O2 well and thus suggests that gas exchange in
the alveoli is good.
FECO2 – Fraction of expired air that
is carbon dioxide (CO2%)
FECO2 is the percent of expired air that
is oxygen. The air that we breathe in
has very little carbon dioxide (0.03%).
As stated previously CO2 is produced as a result of cellular metabolism
and thus most of the CO2 exhaled comes from metabolic processes. Typically the air that we exhale is 2.5-6%
CO2.
VE/VO2 & VE/VCO2 – Ventilatory
equivalent ratio for oxygen and carbon dioxide
The ventilatory equivalent ratio for oxygen is
equal to the pulmonary ventilation (VE) divided by oxygen consumption
(VO2). At the “Anaerobic threshold” when
a significant amount of energy is coming from anaerobic metabolism, there is an
increase in lactic acid in the blood (lactic acid is a by-product of anaerobic
metabolism). In order to keep the blood
from becoming too acidic, ventilation increases and helps us blow off excess
CO2. At this point VE increases at a
higher rate than oxygen consumption and thus this ratio (VE/VO2) begins to
increase. The VE/VO2 can also be used as
an index of ventilatory efficiency. If
the subject’s lungs are very efficient at gas exchange, the subject will not
need a very high VE for a given VO2. The
ventilatory equivalent ratio for carbon dioxide is calculated by dividing
VE/VCO2. Click here to see the response of the
ventilatory equivalent ratios to exercise.
LA –Blood Lactate (lactic acid) &
Anaerobic Capacity
Lactic
acid is one of the products of anaerobic carbohydrate metabolism in the
cells. Because it is a relatively strong
acid, it is usually found in the body in the form of lactate (it dissociates
from its hydrogen ions). The amount of lactic acid in the blood at the end of a
maximal exercise test reflects 1) the intensity of the exercise for the subject
(did the subject give a maximal effort), 2) the degree to which the subject
needed to supplement aerobic energy production with anaerobic energy
production, 3) the subject's lactic acid tolerance. It should be noted that the amount of lactic
acid in the blood at any point in time is dependent on both how much is
entering the circulation (produced) and how much is being removed from the
circulation (cleared). For example,
endurance trained subjects will tend to have lower blood lactate values at any
given running speed, or intensity, than untrained subjects; this difference
owing partly to 1) better ability to use aerobic metabolism in the trained
subjects and 2) a better ability to remove lactate from the circulation. One reason why blood lactate is an important
variable to assess is that the hydrogen ions that result from lactate
production in the cell are known to cause muscle fatigue via several different mechanisms. An athlete who can perform at high
intensities with minimal lactate accumulation in the circulation will be better
able to avoid fatigue. On the other
hand, during high intensity exercise, the ability to use anaerobic energy systems
is very important. Thus, it is not
uncommon to find very high maximal blood lactate values in athletes competing
in high intensity events. Resting blood lactate is typically close to 1 mM, the
anaerobic threshold is said to be around 4 mM, one criterion for a valid VO2max
test is a value exceeding 8 mM, and elite athletes competing in events lasting
2-6 minutes have been reported to have values exceeding 25 mM! Click here to see the blood lactate (LA)
response to exercise. OU
X-C male. OU X-C
female.
The anaerobic
threshold (AT) is an outstanding predictor of endurance performance. It corresponds with the intensity beyond
which progressive increases in blood lactate occur. At intensities lower than
the anaerobic threshold, almost all of the energy needed to perform the
exercise is coming from aerobic energy systems.
At intensities above this "threshold" anaerobic energy
production is needed to supplement aerobic energy production. For an average
person the anaerobic threshold occurs at 50-60% of VO2max. In highly trained runners, the anaerobic
threshold is typically between 75 and 90% of VO2max. There are several ways of assessing anaerobic
threshold. Individuals with a high VO2max
typically also have a high AT, but the relationship between AT and VO2max
is highly variable. Having a high AT is
probably more important for long distance runners and having a high VO2max
is probably more important for mid-distance runners (e.g. 1,500). To be successful,
mid-distance runners also must have a great ability to tolerate high
concentrations of lactic acid. If it appears that VO2max is as high
as it can go for a particular athlete (determined with repeat testing), then
one way the athlete can continue to improve performance would be to modify
their training to focus on improving their AT.
The classic way of assessing the AT is by assessing blood
lactate (LA) continuously throughout the test and identifying the point where
blood LA begins to accumulate (this is also called the lactate threshold). However,
it is not always convenient to take blood lactates throughout the test. Fortunately, there is a non-invasive means of
estimating the AT using the ventilatory response to exercise. The ventilatory threshold can be determined
using several different methods [4]. One of these
methods is to identify the point where the VE/VO2 begins to
continuously increase. Click here
to see how the anaerobic threshold can be determined. OU X-C male. OU X-C female.
Running Economy &
Mechanical Efficiency
Running
economy reflects how efficient an athlete is.
An athlete who is more efficient can run faster for a given oxygen
consumption (VO2). It also
means that if two athletes are running at the same VO2, the one who
is more economical will be able to run faster.
Running economy improves over time and is typically greatest during the
peak competition season.
For more information contact:
Chris
Schwirian
Instructor
of Physiology
Department of Biological Sciences
066
Phone:
(740) 593-9490
Fax:
(740) 593-0300
e-mail:
schwiria@ohiou.ed
web:
http://www.biosci.ohiou.edu/faculty/schwirian/
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Gaskill, BC Ruby, AJ Walker, OA Sanchez, RC Serfass, AS Leon: Validity and reliability of combining three
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Svedenhag, B Sjodin: Physiological
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vol. 7. pp. 329-365. Carmel, IN: Cooper Publishing Group; 1994: 329-365.