WHAT ABOUT V̇O2 MAX?

 

A photo of V̇O2 max Test in 1922.     
    V̇O2max dates back to the early 1920's when it first came to limelight. This was made possible by British physiologists A.V. Hill and Hartely Lupton. During their extensive research on how the muscles work, they discovered that there was a relationship between the amount of oxygen consumed and the output of a physical activity. This over the years has been a key instrument in evaluating cardiorespiratory fitness and endurance capacity. 

   V̇O2 max stands for maximal oxygen consumption. It's used to indicate the maximal rate of oxygen consumed per minute, during physical exertion. When measuring this, we are indirectly calculating the maximal capacity to do work aerobically. During muscular contraction, a lot of ATP (Adenosine Triphosphate) is needed. This means an increase in the demand of oxygen to generate energy. If the measurement indicates more consumption of oxygen, then it's a proof that more muscle cells are contracting and consuming energy.  For this process to happen, our muscles are dependent on two things:

  • An external delivery system that can source out oxygen from the environment to the working muscle cells.
  • Mitochondria to ensure proper utilization of the oxygen by the muscle cells.

An endurance athlete is characterized by a great cardiovascular system and a well-developed oxidation capacity in his/her skeletal muscles. This amounts to a big and efficient cardiac pump, useful in delivering oxygen-rich blood to the muscles.

Muscles and oxygen delivery.

When discussing about V̇O2 max, there are two terms that are constantly repeated i.e. Oxygen delivery and Oxygen utilization.
1) Oxygen delivery is the ability of the cardiovascular system i.e. the heart, blood vessels and blood to transport oxygen from the lungs to the working muscles. Hemoglobin is a key factor for it helps with the transportation of oxygen throughout the body. In a situation where the heart can't pump enough blood or the blood's oxygen-carrying capacity is compromised for example as a result of anaemia, our  V̇O2 max suffers.
2) Oxygen utilization is the ability of how efficiently our muscle cells extract and use oxygen during an exercise. The body has different forms of energy systems, which come into play depending on a few factors like duration. In our case, oxygen/ aerobic form of energy comes into play after the depletion of ATP-PC and lactic acid energy systems which happens approximately after 3 min. If the muscles lack sufficient mitochondria or if their enzymes are sluggish, then the V̇O2 max suffers.

There has been a bone of contention on what really acts as a limiting factor to the V̇O2 max, in reference to the two processes above. Most experts say that  oxygen delivery could be it for the muscle capacity to use oxygen exceeds the heart capacity to deliver.
The heart can't deliver a high volume of blood to all skeletal muscles and still maintain adequate blood pressure.

What are some of the guidelines for testing VO2 max?

In order to determine an individual's true maximal aerobic capacity, exercise conditions must be created to maximally stress the blood delivery to the muscle. This means that:
  • The exercise must employ at least 50% of the total muscle mass.
  • It must be independent of strength, speed, body size and skills.
  • It must be of sufficient duration for cardiovascular response to be measured. ( Exercise protocols are completed between 6-12 min.)
Here are ways of knowing someone has reached their threshold using the treadmill protocol of testing for V̇O2 max:
  • When an increase in intensity doesn't affect the rate of oxygen consumption.
  • When one gets to extreme hyperventilation.
  • When one's maximum heart rate i.e. 220 - (current age) doesn't seem to be affected by an increase in workload.

How to evaluate the result from the assessment.

After the test is done, the result might come out in one of these two forms:
a) Absolute V̇O2max results - it SI unit is in litres per minute. This is more practical for guys in sporting activities where bodily weight isn't really a matter of consideration. A great example is rowing as a sport, where the weight is evenly distributed. It's ideal for comparing the aerobic capacity of individuals in different weight caps. An average man can have a capacity that ranges between  3.0-6.0L/min while for an average woman, it can range between 2.5-4.5L/min. Speaking of elite male athletes, their capacity can range between 5.0-6.5L/min while for their female counterparts, it ranges between 4.0-5.0L/min.  
b) Relative  V̇O2 max results - its SI unit is in milliters per kilogram of body weight per minute. This makes it ideal for sporting activities where every gram of weight could make a difference. A good example is marathon running, where an increase in weight could translate to an increase in energy consumption and can easily slow down efficiency. An average man has the capacity of 35-40ml/kg/min while for the females, it between 27-31ml/kg/min. When it comes to elite male athletes, their capacity ranges between 70-85ml/kg/min while for their females counterparts, it ranges between 60-75ml/kg/min. 


At times, the values can vary depending on a few factors  like age and an individual's fitness level. Genetics has also been proven to be among the most dominating factors. Speaking of physical structure, most elite athletes have a bigger and thicker left ventricle (broadened left side of the heart)  than an average individual. This is what creates the difference between elite athletes and regular individuals when analyzing  V̇O2 max results.




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