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.

AT –Anaerobic Threshold

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 Irvine Hall

Ohio University

Athens, OH 45701

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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2.             American College of Sports Medicine., BA Franklin, MH Whaley, ET Howley: ACSM's guidelines for exercise testing and prescription, 6th edn. Philadelphia: Lippincott Williams & Wilkins; 2000.

3.             RA Boileau, CA Horswill: Body Composition in Sports: Measurement and Applications for Weight Loss and Gain. In: Exercise and Sports Science Edited by WE Garrett, DT Kirkendall. pp. 319-338. Philadelphia, PA: Lipincott Williams & Wilkins; 2000: 319-338.

4.             SE Gaskill, BC Ruby, AJ Walker, OA Sanchez, RC Serfass, AS Leon: Validity and reliability of combining three methods to determine ventilatory threshold. Med Sci Sports Exerc 2001, 33:1841-8.

5.             J Svedenhag, B Sjodin: Physiological characteristics of elite male runners in and off-season. Can J Appl Sport Sci 1985, 10:127-33.

6.             R Maughan: Physiology and Nutrition for Middle Distance and Long Distance Running. In: Perspectives in Exercise Science and Sports Medicine: Physiology and Nutrition for Competitive Sport Edited by DR Lamb, HG Knuttgen, R Murray, vol. 7. pp. 329-365. Carmel, IN: Cooper Publishing Group; 1994: 329-365.