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Performance Testing, Part 1: VO2 max

Updated: Nov 28, 2022

Performance Testing: Why, What and How

As an athlete or coach, why, what and how should you test? This blog series will hopefully give you a better idea of what determines endurance performance, how to test those things, and how to interpret the results to then make an informed training plan for yourself or your athlete. The series will be broken into eight mini-posts, with the odd posts aimed at understanding the parameter we are testing and the even posts describing the actual tests. I hope you enjoy reading this series and are able to take something away and apply it to your own training to improve performance on race day.

Parameters to Test

When it comes to performance tests, the possible variables to test are many and the ways to test them are even more. However, when it comes to markers that give clear insight into performance level and how that performance level is made up, there are four key parameters that come to mind. The first parameter we will explore is the most elemental of the four, and somewhat influences the others.

VO2 max

VO2 max is a household term in the endurance sports world, and rightfully so. Despite the fact that the actual measurement (maximal oxygen uptake) does not particularly matter in itself, the implications are extremely important. By measuring the maximal oxygen uptake of an athlete, we can calculate the maximal rate of aerobic energy production possible in the mitochondria of the athlete’s muscles. The amount of energy an athlete can produce aerobically is, barring mechanical inefficiency, a sure way to predict performance. Knowing the upper limit of this energy production system gives you important information on the athlete’s performance potential, their optimal aerobic training load, and finally, training intensity. Let’s better understand VO2 max to see how we can use it to improve training.

Just as your car’s dashboard has a speedometer that tells you how fast you are driving, your gps watch and power meter tell you how fast you are running or how much power you are putting out. More so, your car’s speedometer has an upper limit. For a 1970’s Jeep, this upper limit may be 80mph. However, a Ferrari’s odometer will max out at a much higher speed. For now, we can view this upper limit of speed as the car’s VO2 max. No matter how hard you push on the accelerator, the car will not go much faster than this speed. Just like the car, no matter how much faster we run or how much harder we push on the pedals, our aerobic energy production will reach a limit. This is where VO2 max occurs. So, how does knowing VO2 max help us predict performance potential?

Just like the car speedometer tells us the maximum speed potential of the car, the VO2 max tells us the maximum aerobic energy production of the athlete. This potential can not be exceeded and takes proper training over time to slowly increase by small margins. Assuming two athletes have the same efficiency and ability to use their VO2 max (fractional utilization of VO2 max), the athlete with the higher VO2 max will win the race. This is because the athlete with the higher VO2 max can simply produce more energy aerobically. So, on a broad scale, VO2 max can be a predictor of endurance performance. In this case, bigger is always better. However, amongst well-trained individuals, VO2 max only goes so far in predicting performance. This is because not every athlete can use the same percentage of their VO2 max for a long time. This is a very important point that we will cover later. For now, know that VO2 max tells us the maximum potential of an endurance athlete. Also, know that this is not the most important information we glean from measuring the VO2 max.

The primary reason to measure VO2 max comes down to optimizing training prescription. Thanks to the work of Professor Aloïs Mader and his human metabolism simulation models, we can calculate the right amount of aerobic stimulus an athlete (the athlete’s mitochondria) need in order to have a maximum adaptation to training. If you know the % of energy coming from aerobic pathways at different power outputs (gained from testing), you can monitor how may kilojoules an athlete burns aerobically, therefore allowing you to know how much work the aerobic system is doing during a session. This is extremely helpful for the coach in terms of monitoring just how much “dose” the athlete’s aerobic system is receiving. With too little training, the athlete will not reach their potential. With too much training, the athlete will never properly adapt to the training and, thus, never reach their potential. Knowing the VO2 max and, thus, the size of the engine and how much “reving“ that engine needs to adapt, gives the coach the information he needs to properly train the aerobic engine.

No less important, knowing the speed/power at VO2 max allows the coach to know just how hard any intensity is stressing the aerobic system. If the speed/power at VO2 max is known, then the coach can calculate what percentage of VO2 max the athlete is working at at any speed or power. Just like your car’s odometer gives you a color indicator of green, yellow, or red behind each RPM value, the % VO2 max gives you the same type of information; how close to maximum is the aerobic engine working?

Some would argue that knowing the %VO2 max of intensities is not important because different athletes can use different percentages of their VO2 max due to differences in metabolisms. This is true. An athlete with a VO2 max of 80ml/kg/min could only be able to use 60% of this value for an hour because they are not metabolically efficient (too much anaerobic contribution, low fat max, etc). On the flip side, an athlete with a VO2 max of 65 could be able to use 85% of this value because they are well trained (lower anaerobic contribution, higher fat max). However, just because the second athlete is able to train/race at a higher % of VO2 max does not change the fact that they are exercising closer to their maximum potential. The fitter athlete can maintain a higher aerobic stress for longer than the unfit athlete, but the fact that they are stressing their aerobic system more doesn’t change. This is why so many athletes train too fast, too often. They are metabolically efficient thanks to a lot of endurance training, so exercising at a high % of VO2 max feels subjectively easy, results in a low HR, and even results in a low blood lactate value. However, due to their good metabolic fitness, they unknowingly stress their aerobic system far too much and too often for it to make optimal adaptations. They feel good but are not improving as fast as possible. Eventually, this leads to performance stagnation. This is why knowing the % of maximum the athlete is working at is a critical piece of the training puzzle. Let’s use a simple car example and then move to an athlete example.

You see two cars driving side by side. The cars are identical in all regards except for the size of the engine, which you can not see from the outside. Both cars can drive 75mph at 3,000rpm for 3 hours starting with a full tank of gas. However, what you can’t see is that car 1 has a maximum speed (VO2 max) of 90mph while car 2 has a max speed of 120mph. Despite the fact that both cars seem to be identical in all regards, car 1 has been driving at a higher percentage of it’s max speed than car 2, even at the same rpm and fuel usage. This car’s engine will burn out, over time, far quicker than car 2’s engine. We can exchange these cars with athletes to make our example more practical.

A coach is prescribing the same workout to two athletes who have nearly identical race performances. Athlete 1 and athlete 2 both have an FTP of 280 watts, they both weigh 145lbs, and they both seem to be at equal fitness levels leading into an important race. So, it would seem acceptable to prescribe both athlete’s a set of 4x10 minutes at 275 watts to help increase each athlete’s “threshold”. However, this could potentially be a disastrous decision by the coach, especially over the long term. If athlete 1 has a VO2 max of 80ml/kg/min and athlete 2 has a VO2 max of 65ml/kg/min, athlete 2 is receiving a much larger aerobic stimulus than is athlete 1. If the coach continues to provide similar workouts to these apparently similar athletes, athlete 1 will have success while athlete 2 will never reach their potential. To avoid this, the coach must understand that, although two athletes may seem quite similar, their fitness levels could be composed very differently, requiring a stark difference in training prescriptions.

I hope this provides clarity on what VO2 max is and why it is important to know the VO2 max of an athlete before prescribing a training plan to them. The key takeaway should be that, without knowing the VO2 max, you are guessing the optimal training load for an athlete and guessing the true impact of most training intensities. In my next post, I will cover the best ways to measure or estimate VO2 max in the lab and the field.

For more information on testing, coaching, or consulting, please feel free to email me at or message on Instagram (@robbie_deckard).

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