What is VO_2max?  How does it relate to performance?  And why does everyone go on about Lance Armstrong’s?

The official definition is the “maximal volume of oxygen extracted from the atmosphere and consumed by the body”.  Or in other words maximal aerobic capacity, or functional limit of the cardiovascular system.  Err… yep, so what’s this got to do with riding your bike?  Living, resting or any movement, whether riding a bicycle or lifting the remote to change the TV channel requires energy.  Our muscles currency for energy is ATP (adenosine triphosphate) and the majority of the time we create ATP using our aerobic system which requires oxygen to do so.  We are always consuming a certain volume of oxygen (VO₂) and the amount we consume and utilise depends on how hard we are working. And we all have a limit that is aptly named our VO_2max.  A summary of the anatomical physiological factors that combine to determine VO_2max is outlined below.

Now, before we talk about how it relates to performance – in particular cycling, we need to know how and what the numbers mean.  Our VO_2max can be expressed in two ways or units.  The first, our “absolute value” is in litres per minute (L×min^-1).  That is, litres of oxygen consumed per minute.  The other expression of VO_2max is relative to our body weight, and is the common measure cited in cycling literature.  Our relative measure is our absolute value (in mls) divided by our body weight, therefore it is expressed in mls per kilogram of body weight per minute (mL×kg^-1×min^-1).  That is mls of oxygen consumed per kilogram of body weight per minute.  At rest we use approximately 3.5 mL×kg^-1×min^-1, however as we move about and work harder this number increases.

Where do you stand in the grand scheme of VO_2max?

As with all things in science, exercise physiologists love to categorize, define and evaluate.  Same goes for cyclists.  According to Jeukendrup et al (2000) male road cyclists are categorized into the performance abilities below based on their physiological characteristics:

Unfortunately few results are available for female cyclists, however the AIS recently published values from elite female road cyclists, with VO_2max values of 3.5 – 3.85 L×min^-1 (57 – 73 mL×kg^-1×min^-1), and peak power output >300 watts.  However New Zealand Elite females tend to be over 4L×min^-1.  These numbers suggest gender definitely affects VO_2max.  Does age affect VO_2max?  The answer to this question is yes.  VO_2max decreases up to 10% per decade after approximately ~27 years of age, however these reductions can be reduced with regular activity.

How do these results compare to the average Joe Bloggs?  Normal sedentary TV watching couch potatoes would struggle to achieve a VO_2max of 40 mL×kg^-1×min^-1.  Compare this is some one who had recently had a heart attack, they are as low as 15-20 mL×kg^-1×min^-1.

Is VO_2max important for Cyclists?

The answer to this question is yes and no.  Yes it is important because all movement, including riding our bicycles requires oxygen to synthesize ATP.  Unfortunately there is a physiological relationship that exists where if we want to ride at a given power output or speed it requires a specific volume of oxygen to be consumed to syntheses enough ATP to produce the power output.  However, VO_2max  rarely limits performance because we rarely ride at maximum.  This was demonstrated in 1988 by an American research group who found no difference in elite and well-trained time trialists at national level, despite vastly different time trial times.  The factor that did distinguish performance was percentage of VO_2max at lactate threshold.  In other words, at what percentage did there anaerobic threshold occur.  Elite rider’s thresholds occurred at 81% versus well-trained riders at 65%, indicating this was an important factor in determining performance in riders with similar VO_2max values.  Peak power output at VO2max has been found to be a very important indicator of time trial performance in well-trained to elite cyclists. 

Big Tex has a Big VO_2max: should he thank his parents or his Coach?

Lance Armstrong reportedly has a VO_2max of 85 mL×kg^-1×min^-1.  This is exceptional and he can thank both his parents and his coach.  It is commonly believed that we cannot change our VO_2max and that is it genetic and you can’t change it ….rubbish!  We all have limits and our genetics do determine how big our upper limit is, but many of us do not achieve it given it lack of training time, knowledge or an understanding of when we have reached it.  The body is a very adaptable organism and Big Tex is a good example of this with his VO_2max decreasing when he had cancer and then increasing again when he started training again.   

Where, How and What to Look out For

The most accurate way to measure VO_2max is by using full gas analysis (as pictured).  This involves wearing a mask, where the volume of air you breathe in is measured and all the air you breathe out is measured for its concentrations of CO₂ and O₂ to calculate vo2max.  Numerous gyms and sports labs use predictive equations based on heart rates achieved at specific power outputs, however these are just that – predictions.  Unfortunately they are derived from regression equations and can easily over or under estimate VO_2max, especially if you have an unusual heart rate response.  They are good indicators for non-athletic people when they first join a gym as there is a certain amount of risk in pushing someone to maximum especially if they are not used to exercise.  However, if you are an athlete you should get it done properly.  Always ensure you do the test on your own bicycle as there is nothing worse for a cyclist than jumping on a gym bike with a tractor saddle and trying to achieve a true maximum. The discomfort of an unfamiliar bike set up will get you before your maximum is achieved and remember a good warm up is essential.  Ensure you do the test in the mode of exercise you want the information for and are most used to.  For example, if you are a cyclist ensure the test is done on a bike, and if you are a runner, on a treadmill.  VO_2max is very specific to the mode of exercise and how familiar you are with that mode of exercise.  For example, if a cyclist who never runs does a running VO_2max they will not achieve as high a on the treadmill as they would on a bike simply because they are not used to running and do not have the necessary motor co-ordination.  How much would you expect to pay for this type of test?  Anywhere from $100 to $250.  There are several sport science laboratories around New Zealand that have appropriate equipment to complete true VO_2max tests.

Amy Taylor is an Auckland based Exercise Physiologist and Cycling Coach.  The founder of Kinetic Edge Cycling Coaching, she was Cycling New Zealand's Personal Coach and Overall Coach of the Year in 2007 and author of the "Lake Taupo Cycle Challenge Guide."  Kinetic Edge can be contacted on 09 368 7819.