Guide to VO2 max by George Evans
We have had the pleasure of George Evans who has been a coached & Team Bottrill rider of Matt's for a few years now come and do a work placement with us for 5 weeks as part of his university degree. He has written a guest post for us on the subject of VO2 Max.
What is VO2 max?
VO2 max or ‘maximal oxygen uptake’ is a term thrown around a lot in the world of endurance sport, especially in the world of cycling and cycling coaching. Let’s explore why and see if it’s as important as it’s made out to be…
The term maximal oxygen uptake was first coined in the 1920’s. It was found that during incremental exercise eventually, however much the work rate was increased beyond a certain point, no further increase in oxygen intake could occur. The point at which one reaches this is deemed to be their VO2 max (Hill & Lupton,1923 ; Bassett & Howley, 2000).
Now VO2 max is defined as:
“the highest rate at which oxygen can be taken up and utilised by the body during severe exercise at sea level” (Bassett & Howley, 2000).
By this definition, it is clear VO2 max is a measure of 2 factors:
• Transport – The functional capacity of the cardio-respiratory system to transport oxygen.
• Utilisation – The maximum ability of the tissues to use oxygen.
These two factors are underpinned by the body’s methods of oxygen (O2) transportation and utilisation. The transportation of O2 is reliant upon and determined by the body’s central cardio-respiratory system. The Utilisation of O2 is reliant upon and determined by the body’s peripheral systems.
There is a series of steps from atmospheric oxygen making its way to the mitochondria via the central and peripheral systems, each one has the potential to be rate limiting:
• The lungs: diffusion of O2 from the alveolus into the pulmonary capillary blood in the lungs.
• The heart: Cardiac output (Q) = Stroke volume x Heart rate.
• Red blood cells – Haemoglobin concentration
• Muscle tissue – peripheral blood flow and extraction of O2 (a-vO2diff)
• Capillary density
• Mitochondrial density
• enzyme concentration
Both factors are represented in the (Fick) equation for VO2 max:
(VO2 = Q × a-vO2diff)
Which factors limit VO2 max the most:
It has been concluded that during whole-body exercise in humans the primary limiting factor of VO2 max is one’s cardio-respiratory system (heart, lungs, blood). Some studies have shown that when using smaller muscle groups or isolating limbs peripheral limitations are more prominent, but it is agreed that the cardio-respiratory system is the main limitation to human VO2 max (Bassett & Howley, 2000).
• Cardiac output: This is usually the primary limiting factor in one’s VO2 max. As exercise increases cardiac output increases to meet the body O2 demands. Both the heart rate and stroke volume of the heart increase linearly with exercise. However, in trained athletes the contribution of stroke volume is more significant due to physical adaptations to the muscular wall of the heart which cause more powerful contractions.
• Pulmonary diffusion capacity (the lungs): This is an interesting one as at sea level the lungs of an average person perform their job of saturating arterial blood with O2 really well. Even during maximal exercise, they manage maintain saturation levels in arteriole blood of around 95%. However trained individuals are more likely to see lower blood O2 saturation levels than regular people at maximal exercise intensities which seems strange. There is a simple explanation, the increased cardiac output trained individuals’ pumps blood around the body with greater force/velocity and therefore there is less transit time for the red blood cells to saturate with O2 in the pulmonary capillary. Due to this, it has been shown highly trained athletes are able to increase their VO2 max significantly in hyperoxia conditions whereas non-trained individuals VO2 maxes remain relatively un-changed. This presence of this increase in VO2 max in O2 rich conditions shows that pulmonary diffusion is indeed a limitation to VO2 max in trained individuals. This limitation becomes more prominent at altitude where the presence of O2 is reduced.
Understanding the numbers
It is common practice to convert VO2 max data from an absolute value - litres of oxygen consumed per minute (L.Min) to a relative value - millilitres of oxygen per kilogram of body mass per minute (ml.kg.min) to nullify the effect weight has on VO2 max. For example, if someone claims a VO2 max of 60 ml.kg.min it means they can transport and utilise 60ml of oxygen per minute for every kg of body mass.
What influences VO2 max?
Genetic contribution for VO2 max is around: 30-50%
A rapid decline in VO2 max occurs when training is ceased, this is mainly down to cardiac output decreasing as a result of a decreased stroke volume, HR isn’t as influenced by training.
Detraining also causes a loss in Plasma volume, haemoglobin and mitochondrial density which all lead to a further decrease in VO2 max.
• Children usually have a similar VO2 max until the age of 12 at which point males VO2 max generally increase faster relative to the female VO2 max.
• VO2 max tends t