VO 2 max (also maximal oxygen consumption, maximal oxygen uptake, peak oxygen uptake or maximal aerobic capacity) is the maximum rate of oxygen consumption measured during incremental exercise; that is, exercise of increasing intensity.[1][2] The name is derived from three abbreviations: "V" for volume, "O 2 " for oxygen, and "max" for maximum. Maximal oxygen consumption reflects the cardiorespiratory fitness of an individual, which is a powerful modifiable determinant of life expectancy in United States adults. It is also an important determinant of endurance capacity during prolonged exercise.

Relationship to cardiovascular disease and life expectancy [ edit ]

VO 2 max is widely used as an indicator of cardiorespiratory fitness. In 2016, the American Heart Association published a scientific statement[3] recommending that cardiorespiratory fitness (CRF), quantifiable as VO 2 max, be regularly assessed and utilized as a clinical vital sign. This statement was based on mounting evidence that lower fitness levels are associated with high risk of cardiovascular disease, all-cause mortality, and mortality rates stemming from various types of cancers. In addition to risk assessment, the AHA recommendation cited the value measuring fitness for validating exercise prescription, physical activity counseling, and improving both patient management and patient health.

Expression [ edit ]

VO 2 max is expressed either as an absolute rate in (for example) litres of oxygen per minute (L/min) or as a relative rate in (for example) millilitres of oxygen per kilogram of body mass per minute (e.g., mL/(kg·min)). The latter expression is often used to compare the performance of endurance sports athletes. However, VO 2 max generally does not vary linearly with body mass, either among individuals within a species or among species, so comparisons of the performance capacities of individuals or species that differ in body size must be done with appropriate statistical procedures, such as analysis of covariance.[2]

Measurement and calculation [ edit ]

Measurement [ edit ]

2 max measurement using instruments on a modern metabolic cart during a graded treadmill exercise test VOmax measurement using instruments on a modern metabolic cart during a graded treadmill exercise test

Accurately measuring VO 2 max involves a physical effort sufficient in duration and intensity to fully tax the aerobic energy system. In general clinical and athletic testing, this usually involves a graded exercise test (either on a treadmill or on a cycle ergometer) in which exercise intensity is progressively increased while measuring:

ventilation and

oxygen and carbon dioxide concentration of the inhaled and exhaled air.

VO 2 max is reached when oxygen consumption remains at a steady state despite an increase in workload.

Calculation: the Fick equation [ edit ]

VO 2 max is properly defined by the Fick equation:

V O 2 m a x = Q × ( C a O 2 − C v O 2 ) {\displaystyle \mathrm {VO_{2}\;max} =Q\times \ (\mathrm {C_{a}O_{2}} -\mathrm {C_{v}O_{2}} )}

where Q is the cardiac output of the heart, C a O 2 is the arterial oxygen content, and C v O 2 is the venous oxygen content.

(C a O 2 – C v O 2 ) is also known as the arteriovenous oxygen difference.[4]

Estimation using submaximal exercise testing [ edit ]

The necessity for a subject to exert maximum effort in order to accurately measure VO 2 max can be dangerous in those with compromised respiratory or cardiovascular systems; thus, sub-maximal tests for estimating VO 2 max have been developed.

The heart rate ratio method [ edit ]

An estimate of VO 2 max is based on maximum and resting heart rates.[5] It is given by:

V O 2 max ≈ HR max HR rest × 15.3 mL / ( kg·minute ) . {\displaystyle {\text{V}}{\ce {O2}}{\text{ max}}\approx {\frac {{\text{HR}}_{\text{max}}}{{\text{HR}}_{\text{rest}}}}\times 15.3{\text{ mL}}/({\text{kg·minute}}).}

This equation uses the ratio of maximum heart rate (HR max ) to resting heart rate (HR rest ) to predict VO 2 max. The researchers cautioned that the conversion rule was based on measurements on well-trained men aged 21 to 51 only, and may not be reliable when applied to other sub-groups. They also advised that the formula is most reliable when based on actual measurement of maximum heart rate, rather than an age-related estimate.

Cooper test [ edit ]

Kenneth H. Cooper conducted a study for the United States Air Force in the late 1960s. One of the results of this was the Cooper test in which the distance covered running in 12 minutes is measured. Based on the measured distance, an estimate of VO 2 max [in mL/(kg·min)] is:[6]

V O 2 m a x ≈ d 12 − 504.9 44.73 {\displaystyle \mathrm {VO_{2}\;max} \approx {d_{12}-504.9 \over 44.73}}

where d 12 is distance (in metres) covered in 12 minutes

An alternative equation is:

V O 2 m a x ≈ ( 35.97 ∗ d m i l e s 12 ) − 11.29 {\displaystyle \mathrm {VO_{2}\;max} \approx {(35.97*dmiles_{12})-11.29}}

where dmiles 12 is distance (in miles) covered in 12 minutes,

Multi-stage fitness test [ edit ]

There are several other reliable tests and VO 2 max calculators to estimate VO 2 max, most notably the multi-stage fitness test (or beep test).[7]

Rockport fitness walking test [ edit ]

Estimation of VO 2 max from a timed one-mile track walk with duration t, incorporating gender, age, body weight in pounds (BW), and heart rate (HR) at the end of the mile.[8] The constant x is 6.3150 for males, 0 for females. BW is in lbs, time is in minutes.

V O 2 m a x ≈ 132.853 − 0.0769 B W − 0.3877 age − 3.2649 t − 0.1565 H R + x {\displaystyle \mathrm {VO_{2}\;max} \approx 132.853-0.0769BW-0.3877{\text{age}}-3.2649t-0.1565HR+x}

Firstbeat method [ edit ]

The Firstbeat method of VO 2 max estimation, of which a patent application was filed in 2012,[9] is widely licensed and used in consumer technology applications.[10] The first consumer fitness device utilizing the Firstbeat method of VO 2 max estimation was the Garmin Forerunner 620, released in 2013.[11] Since then, Suunto, Jabra, Huawei, and PulseOn[12] have also introduced products that utilize the Firstbeat method.[13]

The method relies on an analysis of the linear relationship between oxygen consumption and running speed, meaning that the oxygen cost of running increases when running speed increases. To facilitate analysis and enhance accuracy, timed segments of recorded activity data are identified on the basis of heart rate ranges and reliability; and only the most reliable segments are utilized. This allows the method to be applied to freely performed running, walking and cycling activities and diminishes the need for dedicated fitness testing protocols. The calculation requires user basic anthropometric data (age, gender, height, weight, etc.), heartbeat data (internal workload), and a measure of external workload.[14]

External workload running/walking: movement speed obtained from either GPS or accelerometer sensors

External workload cycling: power output expressed in watts and measured by a power meter.

VO 2 max estimates provided by the Firstbeat method are most accurate during running activities that utilize GPS to capture external workload data. This combination has been validated to be 95% accurate compared to laboratory testing.[14] Because the Firstbeat estimation method is sub-maximal in nature, accuracy of the estimate is strongly tied to validity of the HRmax value used in the calculation.[14]

Effect of training [ edit ]

The average untrained healthy male has a VO 2 max of approximately 35–40 mL/(kg·min).[15][16] The average untrained healthy female has a VO 2 max of approximately 27–31 mL/(kg·min).[15] These scores can improve with training and decrease with age, though the degree of trainability also varies very widely: conditioning may double VO 2 max in some individuals, and will never improve it in others.

Athletes [ edit ]

In sports where endurance is an important component in performance, such as cycling, rowing, cross-country skiing, swimming and running, world-class athletes typically have high VO 2 maxima. Elite male runners can consume up to 85 mL/(kg·min), and female elite runners can consume about 77 mL/(kg·min).[17] Five time Tour de France winner Miguel Indurain is reported to have had a VO 2 max of 88.0 at his peak, while cross-country skier Bjørn Dæhlie measured at 96 mL/(kg·min).[18] Dæhlie's result was achieved out of season, and physiologist Erlend Hem who was responsible for the testing stated that he would not discount the possibility of the skier passing 100 mL/(kg·min) at his absolute peak. Norwegian cyclist Oskar Svendsen is thought to have recorded the highest VO 2 max of 97.5 mL/(kg·min), when aged 18.[19]

The highest values in absolute terms for humans are often found in rowers, as their much greater bulk makes up for a slightly lower VO 2 max per kg. Elite oarsmen measured in 1984 had VO 2 max values of 6.1±0.6 L/min and oarswomen 4.1±0.4 L/min.[20] Rowers are interested in both absolute values of VO 2 max and in lung capacity, and the fact that they are measured in similar units means that the two are often confused. British rower Sir Matthew Pinsent is reported to have had a VO 2 of 7.5 L/min[21] . He also had a lung capacity of 8.5 litres.[22] New Zealand sculler Rob Waddell has one of the highest absolute VO2 max levels ever tested.[23] These VO2max figures are absolute figures (ie the total amount of oxygen metabolised in a minute). Rowers tend to be more interested in absolute VO2max whereas runners are generally more interested in relative VO2 max (ie the total amount of oxygen metabolised per minute per kilogram of body weight)[24].

Other animals [ edit ]

VO 2 max has been measured in other animal species. During loaded swimming, mice had a VO 2 max of around 140 mL/(kg·min),[25] Thoroughbred horses had a VO 2 max of around 193 mL/(kg·min) after 18 weeks of high-intensity training.[26] Alaskan huskies running in the Iditarod Trail Sled Dog Race had VO 2 max values as high as 240 mL/(kg·min).[27] Estimated VO 2 max for pronghorn antelope was as high as 300 mL/(kg·min).[28]

Limiting factors [ edit ]

The factors affecting VO 2 are often divided into supply and demand.[29] Supply is the transport of oxygen from the lungs to the mitochondria (including lung diffusion, stroke volume, blood volume, and capillary density of the skeletal muscle) while demand is the rate at which the mitochondria can reduce oxygen in the process of oxidative phosphorylation.[29] Of these, the supply factor is often considered to be the limiting one.[29][30] However, it has also been argued that while trained subjects probably are supply limited, untrained subjects can indeed have a demand limitation.[31]

Factors that affect VO 2 max are: age, sex, fitness and training, altitude, and action of the ventilatory muscles.[32] VO 2 max can be a poor predictor of performance in runners due to variations in running economy and fatigue resistance during prolonged exercise.[32]

Cardiac output, pulmonary diffusion capacity, oxygen carrying capacity, and the peripheral limitations of muscle diffusion capacity, mitochondrial enzymes, and capillary density are all examples of VO 2 max determinants. The body works as a system. If one of these factor is sub-par, then the whole system loses its normal capacity to function properly.[31]

The drug erythropoietin (EPO) can boost VO 2 max by a significant amount in both humans and other mammals.[33] This makes EPO attractive to athletes in endurance sports, such as professional cycling. EPO has been banned since the 1990s as an illicit performance-enhancing substance. But in 1998 it became widespread in cycling and led to the Festina affair[34][35] as well as being mentioned ubiquitously in the USADA 2012 report on the US Postal team.[36] Greg LeMond has suggested establishing a baseline for riders' VO 2 max (and other attributes) to detect abnormal performance increases.[37]

History [ edit ]

British physiologist Archibald Hill introduced the concepts of maximal oxygen uptake and oxygen debt in 1922.[38][30] Hill and German physician Otto Meyerhof shared the 1922 Nobel Prize in Physiology or Medicine for their independent work related to muscle energy metabolism.[39] Building on this work, scientists began measuring oxygen consumption during exercise. Notable contributions were made by Henry Taylor at the University of Minnesota, Scandinavian scientists Per-Olof Åstrand and Bengt Saltin in the 1950s and 60s, the Harvard Fatigue Laboratory, German universities, and the Copenhagen Muscle Research Centre among others.[40][41]

See also [ edit ]