Symptoms Of Low VO2 Max

In this article, we will take a close look at VO2 max. This measure of fitness is of interest to anyone who wishes to improve their cardiovascular health. We will explore the symptoms of low VO2 max, factors that can cause it to decrease, and methods to improve it. We will also look at certain common drugs that can influence the VO2 max.
Jakub Gwiazdecki

Jakub Gwiazdecki

Fifth year medical student at the Medical Faculty of Comenius University in Bratislava.

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What are the symptoms of low VO2 max?

The first noticeable symptom of low VO2 max is shortness of breath. This occurs during strenuous physical activity that pushes beyond the body's limit to use oxygen effectively. Such a situation can take place, especially during high-intensity exercise [1, 2].

The shortness of breath is often accompanied by a very fast breathing rate during and shortly after the exercise [3].

Walking past the VO2 max limit leaves the body fatigued. When the border of effective oxygen utilization is low, these symptoms can occur after what is generally considered light exercise [1, 4].

Low VO2 max can also lead to arrhythmia during or after training [2, 4]. Individuals with preexisting respiratory diseases, like chronic lung disease, can experience coughing [1].

When the body's limit is exceeded severely, the brain and the heart do not receive sufficient blood. Lack of oxygen in those two vital organs can lead to confusion and unconsciousness [2].

Lastly, another symtpom of low VO2 max is cyanosis. It is a condition when the blood deoxygenation reaches high enough levels to become visible. Cyanosis needs medical attention and can be recognized by bluish-colored lips, fingernails, and peripheral skin [2, 5].

What is VO2 max?

VO2 max, or maximal volume oxygen uptake, is the maximum rate of oxygen the muscles, brain, and heart can use during intense exercise. It allows for measuring the body’s maximum ability to take in and use oxygen effectively to generate energy [4, 6]. VO2 max is measured and expressed in mL/kg/min.

This measure is often associated with professional athletes only. However, in reality, it is a great way to assess the cardiovascular health of anyone [6].

High values of VO2 are beneficial at any age. The higher the volume of oxygen that the body can use, the more energy is available, and so is the stamina. With a high VO2, the body can easily handle aerobic physical activity like running [6].

Essentially, VO2 max reflects the athletic performance one can deliver, and a higher level is an indicator of better performance [6].

What can cause the VO2 max to fall?

The primary factor that negatively impacts VO2 is severe acute hypoxia (low oxygen levels in the blood). This condition decreases the levels of available oxygen in the arterial blood by more than one-third. Combined with a subsequent decrease in cardiac peak output and blood flow to the legs, hypoxia causes a significant reduction in VO2 max [7].

Another factor is physiological, which is impossible to bypass. Age impacts the whole body and its processes, so there should be no wonder that it also impacts the VO2 max. Every year, the maximum oxygen capacity that can be used in the human body declines by around 0.43 ml/kg/min in men and 0.3 ml/kg/min in women [8].

Also, a long bedtime can reduce the VO2 max. The adaptation of the cardiac output and stroke volume to the flat position of the body results in lower performance when in the upright position [9]. This applies especially to individuals who stop any physical activity due to, for example, a hospital stay.

Intoxication with carbon monoxide (CO) can lower the VO2 max to a great extent. After the carbon oxide binds to the erythrocytes, it creates carboxyhemoglobin (HbCO). This new form of the red blood cell cannot bind oxygen. As a direct result of CO binding irreversibly to the red blood cells, the oxygen transport capacity of the blood decreases. A significant reduction in the VO2 levels can be felt already at a HbCO blood concentration of 7% [10].

How can the VO2 max be improved?

Improvement of the VO2 max can be achieved through various methods.

One very effective way to improve the VO2 max is by exercising at maximum heart rate. Physical activity at this level strengthens the heart, increasing the volume of the ejected blood and the VO2 max. To make the cardiac muscle stronger, training at around 90% of the maximum heart rate is recommended [11].

Fun fact

The maximum heart rate = 220 – your age (approximately)

When speaking in terms of training strategies, a great way to improve the VO2 max is through continuous aerobic exercise. However, even more effective is high-intensity interval training (HIIT). It is another effective way, which is a combination of high-intensity activities with breaks for rest [4].

Can some drugs cause a lower VO2 max?

Yes, certain drugs can indeed cause a decrease in maximal oxygen consumption. One such class of drugs are beta-adrenergic blockers, more popularly known as beta blockers. They can decrease heart rate, as well as VO2 max [12].

Also, diazepam, a drug used in the treatment of anxiety, alcohol withdrawal, and seizures, decreases VO2 max. After the administration, the sedative effect this drug has on the whole body also impacts the heart. The VO2 max decreases by around 8% already after the administration of diazepam [13].

Dobutamine is the next drug that causes maximal oxygen consumption to decrease. It is used in patients with congestive heart failure and leads to an increase in oxygen consumption, thus limiting the availability of oxygen in the blood and negatively impacting the VO2 max [14].

Does Zone 2 training improve VO2 max?

It is not easy to answer this question straight because research on this topic does not address Zone 2 specifically. However, some conclusions can be drawn from the general available studies.

What are the zones of training?

  • Zone 1: 50–60% of maximum heart rate normally can be seen during the warm-up [15].
  • Zone 2: 60–70% of maximum heart rate occurs during longer and higher intensity [15].
  • Zone 3: 70–80% of maximum heart rate; this is the moderate zone of a fast workout. It's a moderate-intensity zone, often used for tempo workouts and longer intervals [15].
  • Zone 4: 80–90% of maximum heart rate is a high-intensity zone that is entered during short and fast workouts [15].
  • Zone 5: 90–100% of maximum heart rate; it is the highest intensity zone, and it occurs during short and extreme exercise [15].C$

While the most effective VO2 increase is high-intensity interval training (HIIT) [4], it does not say the other and potentially lower zone training are not good for VO2. Lower-zone physical acidity can also be very effective. For example, Zone 3 training in a hypoxic environment increases its positive influence compared to the same zone with normal oxygen in the air [16]. Such a boost can be applied to zone 2 upwards and can be achieved by, for instance, moving the activity to high altitudes, where the oxygen concentration is lower [17]

Simple zone 2 activity exercises will increase the level of VO2 to a certain degree, but not in all cases. The effect depends on the general status of the person performing the training. It will be different when a person aged 45 years after surgery with a recovery phase of 2 months performs it when compared to a marathon runner aged 25, who for the last 4 years was running daily. The athlete will not be able to increase his VO2 max level. However, the 45-year-old individual, after 2 months of bedtime, will be able to increase his performance quite well. Of course, to reach his highest VO2, he will have to change to higher zones, but this does not exclude an initial increase in the maximal volume of oxygen uptake.

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Jakub Gwiazdecki

Jakub Gwiazdecki

Jakub is in his fifth year as a medical student at Comenius University in Bratislava, Slovakia. He has special interested in cardiology and in patient-centered medicine. His love for heart health isn't just book-smarts; he wants to know how it works, what it means for our feelings, and how key it is for health and happiness. Jakub thinks real good health care comes from always putting the patient at the centre, treating each person as a whole.