VO₂ max

VO₂ max measurement using instruments on a metabolic cart during a graded treadmill exercise test

Gas exchange of VO₂ and VCO₂ during max test. Begin for 3 minutes at 60 watts and add 35 watts every 3 mins until exhaustion.

Accurately measuring V̇O₂ 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.

The classic V̇O₂ max, in the sense of Hill and Lupton (1923), is reached when oxygen consumption remains at a steady state ("plateau") despite an increase in workload. The occurrence of a plateau is not guaranteed and may vary by person and sampling interval, leading to modified protocols with varied results.[3]

V̇O₂ may also be calculated by the Fick equation:

${\displaystyle {\ce {{\dot {V}}O2}}=Q\times \ (C_{a}{\ce {O2}}-C_{v}{\ce {O2}})}$, when these values are obtained during an exertion at a maximal effort.

where Q is the cardiac output of the heart, C_aO₂ is the arterial oxygen content, and C_vO₂ is the venous oxygen content.

(C_aO₂ – C_vO₂) is also known as the arteriovenous oxygen difference.

The Fick equation may be used to measure VO₂ in critically ill patients, but its usefulness is low even in non-exerted cases.[5] Using a breath-based VO₂ to estimate cardiac output, on the other hand, seems to be reliable enough.[6]

An estimate of V̇O₂ max is based on maximum and resting heart rates.[7] It is given by:

${\displaystyle {\ce {{\dot {V}}O2}}\max \approx {\frac {{\text{HR}}_{\max }}{{\text{HR}}_{\text{rest}}}}\times 15.3{\text{ mL}}/({\text{kg}}\cdot {\text{minute}})}$

This equation uses the ratio of maximum heart rate (HR_max) to resting heart rate (HR_rest) to predict V̇O₂ 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.

In around 40-year-old normal weight never-smoking men with no cardiovascular diseases, bronchial asthma, or cancer, the HR_max to HR_rest ratio should be multiplied by approximately 14 to estimate V̇O₂ max.[8] Every 10 years of age reduces the coefficient by one, as well as does the change in body weight from normal weight to obese or the change from never-smoker to current smoker. Consequently, V̇O₂ max of 60-year-old obese current smoker men should be estimated by multiplying the HR_max to HR_rest ratio by 10.

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 V̇O₂ max [in mL/(kg·min)] is:

${\displaystyle {\ce {{\dot {V}}O2}}\max \approx {d_{12}-504.9 \over 44.73}}$

where d₁₂ is distance (in metres) covered in 12 minutes.

An alternative equation is:

${\displaystyle {\ce {{\dot {V}}O2}}\max \approx {(35.97*d'_{12})-11.29}}$

where d′₁₂ is distance (in miles) covered in 12 minutes.

There are several other reliable tests and V̇O₂ max calculators to estimate V̇O₂ max, most notably the multi-stage fitness test (or beep test).[9]

Estimation of V̇O₂ max from a timed one-mile track walk incorporating duration in minutes and seconds (t, e.g.: 20:35 would be specified as 20.58), gender, age, body weight in pounds (BW), and heart rate in 10 sec (HR) at the end of the mile.[10] The constant x is 6.3150 for males, 0 for females. BW is in lbs, time is in minutes.

${\displaystyle {\ce {{\dot {V}}O2}}\max \approx 132.853-0.0769\cdot {\text{BW}}-0.3877\cdot {\text{age}}-3.2649t-0.1565\cdot {\text{HR}}+x}$

The average untrained healthy male has a V̇O₂ max of approximately 35–40 mL/(kg·min).[11][12] The average untrained healthy female has a V̇O₂ max of approximately 27–31 mL/(kg·min).[11] These scores can improve with training and decrease with age, though the degree of trainability also varies widely.[13]

In sports where endurance is an important component in performance, such as road cycling, rowing, cross-country skiing, swimming, and long-distance running, world-class athletes typically have high V̇O₂ max values. Elite male runners can consume up to 85 mL/(kg·min), and female elite runners can consume about 77 mL/(kg·min).[14]

High values in absolute terms for humans may be found in rowers, as their greater bulk makes up for a slightly lower V̇O₂ max per body weight. Elite oarsmen measured in 1984 had V̇O₂ max values of 6.1±0.6 L/min and oarswomen 4.1±0.4 L/min.[15] New Zealand sculler Rob Waddell has one of the highest absolute V̇O₂ max levels ever tested.[16]

V̇O₂ max has been measured in other animal species. During loaded swimming, mice had a V̇O₂ max of around 140 mL/(kg·min).[17] Thoroughbred horses had a V̇O₂ max of around 193 mL/(kg·min) after 18 weeks of high-intensity training.[18] Alaskan huskies running in the Iditarod Trail Sled Dog Race had V̇O₂ max values as high as 240 mL/(kg·min).[19] Estimated V̇O₂ max for pronghorn antelopes was as high as 300 mL/(kg·min).[20]