Wednesday, 22 June 2011

Time to Exhaustion at VO2 Max- is it a reproducible measure for cyclists?

VO2 max and Cycling Economy

VO2 max is a benchmark of fitness that most endurance athletes are keenly aware of.  It is the measure of the maximum ability of an athlete’s body to transport and utilize oxygen, typically expressed in the units of ml/min/kg (volume of oxygen used, per minute, per kg of body weight).  So, very simply put, the more oxygen your body is using, and the lighter you are, the higher your VO2 max is.  

Various sources have reported Lance Armstrong’s VO2 max was approximately 85 ml/min/kg during his winning years, while the average 20 year old man’s is approximately 45 ml/min/kg.  The higher your VO2 max, the better you will likely perform.  

So, why even hold races?  Why not just test everybody’s VO2 max, and the highest wins?  While this measure of fitness is a great predictor of performance, it does not tell the entire story.  In cycling, factors such as nutrition, equipment, aerodynamics, drafting, and tactics come into play.  However, even if all of these influences are held constant, VO2 max still does not predict who wins the race.  

Another very important factor, referred to as cycling economy, plays a critical role in predicting performance.  Cycling economy is essentially the measure of how efficiently one’s musculature utilizes the oxygen delivered to transfer power into the pedals.  It is one factor that will allow a cyclist with a lower VO2 max to beat one with a higher VO2 max.


A  great test scientists use to predict performance in cyclists that takes into account both VO2 max and cycling economy is to measure their time to exhaustion.  This involves the simple task of timing how long an athlete can last cycling while working at their VO2 max.  In a 2011 study published in the Journal of Exercise Physiology, 17 competitive cyclists went through the time to exhaustion test to see if it is reproducible.  In other words, if you test your time to exhaustion on one day, will it be the same a week later?  This is what they found:

On the left of the graph (y-axis) we see the difference between the two trials, while the bottom (x-axis) shows the average of the two time to exhaustion trials for each athlete.  For 10 of the 17 athletes, their time to exhaustion increased when comparing the second trial to the first.  Of the 7 remaining athletes, there was very little difference between their first and second trials.  On average, the first time to exhaustion trial measured 223.2 ± 31.3 seconds, while the second trial measured 238.6 ± 33.5 seconds.  In other words, the athletes lasted longer at their VO2 max the second time around.


So why is this?  This study was actually very well designed in that it measured other physiological factors that could explain this significant change including maximum heart rate, VO2 max reached, and blood lactate levels.  Interestingly, all of these measures were constant between trials.

So if the riders were lasting longer, and it was not for physiological reasons, the authors propose that only leaves the rider’s psychology.  Essentially, the riders were able to last longer not because their bodies were better equipped to do so, but their minds were.

So is the time to exhaustion a reproducible test?  From a physiological standpoint it seems that all factors are reproducible.  However, due to psychological factors, it seems inevitable that an athlete will have the potential to improve without actually developing better fitness.

My Analysis

Firstly, keep in mind that this is just one study with a small sample size of only 17 riders.  In addition, the study only measured the time exhaustion on two separate occasions.  It would be interesting to know what impact more athletes and more trials would have on the results.  Maybe the times would then be more consistent.

On a side note, one part of this paper that I found very interesting was the influence of psychology on performance.  This article indirectly shows the importance of mental preparation and toughness during competition.  Getting faster without improving my fitness?  Sounds good to me!


Costa et. al., 2011. Reproducibility of Cycling Time to Exhaustion at VO2 Max in Competitive Cyclists. Journal of Exercise Physiology14:28-34

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