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VO2 and VO2Max: Understanding Oxygen Consumption in Fitness

VO2 stands for oxygen uptake capacity, and VO2Max stands for maximal oxygen uptake capacity. VO2Max indicates how much oxygen the human body can transport and utilize per unit of time during maximal exertion. VO2Max provides a very good indication of an individual’s cardiorespiratory fitness. VO2Max is expressed in the number of milliliters of oxygen per kilogram of body weight per minute (ml/kg/min). In this article, we will delve into the terms VO2 and VO2Max.

What is VO2

ATP (adenosine triphosphate) is the energy form of cells in the body, and there is only a small stored supply that can be used without oxygen intake. ATP is the fuel for the muscles, and muscle cells require oxygen to generate ATP.

Factors influencing VO2 include:

• lung ventilation
• diffusion of oxygen in the lungs to the pulmonary capillaries
• cardiac output
• blood flow to skeletal muscles
• oxygen consumption by skeletal muscles

Also read the article: The ATP-CP System / Phosphate System

Lung Ventilation

Lung ventilation is 20-25 times higher during VO2Max than at rest. During exercise, ventilation increases due to deeper breathing (greater volume) and, during more intense training, mainly due to an increase in breathing frequency.

Gas Exchange

Air consists of approximately 78% nitrogen gas and 21% oxygen gas. In red blood cells, you find hemoglobin that absorbs oxygen and transports it to other cells in the body. During exercise, hemoglobin saturation is approximately 95% in healthy adults. In other words, 95% of the oxygen inhaled is absorbed into the blood.

Cardiac Output

Heart rate increases during exercise because the body, especially the muscles, requires more oxygen. When the heart beats faster, more blood can be processed, leading to more oxygen being transported. Maximum heart rate is reached before maximum VO2 is reached. An individual’s maximum heart rate decreases with age (220 – age = maximum heart rate). With frequent aerobic training, resting heart rate can decrease by 10-15 beats per minute. The stroke volume (amount of blood pumped per heartbeat) of the heart increases with aerobic conditioning training when at rest, during exercise, and during maximal exercise. Cardiac output also increases through aerobic conditioning training.

Oxygen Consumption

Skeletal muscles require more oxygen during exercise. Different muscle types consume different amounts of oxygen. It depends on the proportion of type 1, slow-twitch, muscle fibers or type 2, fast-twitch, muscle fibers in your body, as slow-twitch fibers can consume more oxygen. During maximal training, approximately 85% of the oxygen is absorbed from the blood and used by the skeletal muscles. Through training, this process becomes more efficient because more blood can be delivered, mitochondria become larger and increase in number (they convert oxygen into energy), there is more oxidative enzyme activity (increase in the number of chemical reactions that increase VO2), and there is a higher myoglobin content (more oxygen can be stored in muscles).

Increasing and Improving VO2Max

Conditioning training such as 150 minutes per week of low-intensity training, but also 75 minutes per week of high-intensity training, will improve your VO2Max. An ideal form of training to increase VO2Max is High Intensity Training. High Intensity Training is an explosive training variant in which almost maximal effort is exerted (90% or more of VO2Max) for a short duration. Then, less intense training is performed (rest period) before returning to almost maximum training capacity. Many untrained individuals can often train harder and achieve more through HIT than they would with prolonged moderate-intensity training.

Factors affecting VO2Max include:

Genetics:
Amount of Type 1 and Type 2 muscle fibers
The amount of hemoglobin in the blood

Age:
VO2Max is highest at around 18 years old and remains about the same until around 25. Then, it decreases by about 1% per year. There is a negative correlation between age and VO2Max. However, training can help maintain VO2Max quite well.

Body composition:
People with more muscle tissue will have a higher VO2Max because muscle tissue consumes more oxygen than fat tissue.

Gender:
Men have approximately a 10% to 25% higher VO2Max capacity than women, mainly due to differences in the size of contracting muscles.

Testing VO2Max:
VO2Max can be tested in various ways. There are the 1-mile walk test and the 1.5-mile run test. This can be done outdoors or on a treadmill.