VO2 Max Testing by kyle ruth

This past week we posted the above picture of TTT athlete Steven Playtek completing one of three laboratory VO2max tests. This generated quite a few questions on our social media platforms regarding endurance assessments. I felt that the TTT blog would be a better forum to discuss this topic so for this week we are going to dig into some field assessments that we can use to determine an athlete’s endurance capacity.

Defining Terminology

We first need to define a couple of important terms. I feel that one of the major issues that I run into when discussing program development, particularly endurance development, with other coaches is that we use endurance terminology incorrectly. For example, most coaches and athletes in the sport use the terms: endurance, aerobic, cardiorespiratory endurance, and engine interchangeably, however each of these refers to a different component of our physiology that interacts to determine an athlete’s endurance capacity (with the exception of “engine” which doesn’t really have a formal definition).

Note: if you already have a good understanding of these terms just quickly skim this section and move on to the testing protocols.

Endurance - an athlete’s ability to perform a given task repeatedly at the specific pace or duration required without excessive fatigue. There are a number of different sub-categories that fall under the “endurance” umbrella including: cardiorespiratory endurance, aerobic endurance, anaerobic endurance (or speed-endurance), and local muscular endurance. Each of these terms again looks at a different component or time-domain of endurance performance.

Aerobic - the term “aerobic” when discussing endurance training refers to the aggregate physiological process of converting stored fuel substrates (typically fats and carbohydrates) into usable energy (ATP) by utilizing oxygen delivered to working tissues. Athletes who have a well-developed aerobic system are able to produce energy aerobically at a greater rate than other athletes. This can have a number of benefits but the primary from a performance standpoint is that: given the same level of skill-development the more aerobically fit athlete will be able to maintain a greater rate of work throughout an event without fatiguing. In essence developing a powerful aerobic system creates “fatigue-resistant athletes” as aerobic metabolism is not self-limiting (like the anaerobic-lactic system).

Anaerobic - the anaerobic energy-system can be broken down into two components, the ATP/CP system (I’m not going to go into depth here as this is covered extensively in the upcoming TTT educational courses) and the glycolytic-lactic system. The glycolytic-lactic system produces energy (ATP) by breaking down stored muscle glycogen or blood glucose (our bodies storage and transport forms of carbohydrate) and produces lactic acid as well as a number of other “metabolic wastes”. The anaerobic system is very powerful when compared to the aerobic system from an energy production standpoint however it is self-limiting. As more energy is produced anaerobically, muscle and eventually blood acidity begin to rise. The enzymes that drive anaerobic metabolism operate at a very specific acid/base balance so when the acidity level climbs the rate of anaerobic energy production begins to fall. For anaerobically-powerful athletes this often means a reduction in work-rate or pace as they have a larger gap between their anaerobic power and aerobic power.

Cardiorespiratory (cardio) - refers to the oxygen delivery capacity of the heart, lungs, and vascular system. An individual’s cardiorespiratory capacity refers to their ability to effectively deliver O2 to working tissues (as well as remove metabolic wastes like H+ and CO2). As we’ve discussed on this blog before there can be a mismatch between delivery (cardiorespiratory) and utilization (aerobic) which can create premature fatigue in athletes where one of the two systems is challenged beyond its capacity. Development of both the cardiorespiratory and aerobic systems is critical to developing elite-levels of endurance.

Endurance Testing

Most of us are not fortunate enough to have access to the equipment needed to run a VO2max or lactate threshold test. However we can implement a series of “field tests” to give us information about the development of different physiological markers in our athletes. In order to gather physiological information from a test we have to eliminate as many confounding variables as possibly (basically make it as simple as possible) and ensure that the test can be repeated. In the case of most endurance field tests, this means that we will implement a single cyclical modality. By choosing cyclical modalities we allow ourselves as coaches to gather pacing or power-output data as well as eliminate skill limitations that would cloud our interpretation of the results.

Imagine trying to test an athlete’s endurance capacity using a 7min AMRAP of 7 Thrusters + 21 Double-unders. During their first test they were just learning how to do double-unders, and are just able to manage 6 rounds of the test. Three months later you retest the same athlete, only this time you implemented a good training design and dealt with their double-under limitations during that period. On their retest they blow it out and hit 9 rounds of the test. They are super excited because their endurance has improved dramatically over the past three months!! Or did it? Was their improvement on the retest really due to an increase in endurance capacity or was it due to their improvement in double-under proficiency? This highlights an issue with mixed-modal testing for athlete assessment. Keep in mind, I am in no way saying that you should avoid mixed-modal testing as this IS OUR SPORT. What I am saying is that if your goal is to improve a specific physiological construct that impacts performance, you need to keep your tests as simple as possible. Again, the soon to be released TTT Assessment Course will layout in detail the construction and interpretation of complete athlete testing protocols.

This begs the question: what do we need to know in order to improve an athlete’s aerobic capacity with relation to CrossFit™. I think that a relatively complete endurance testing battery would give us information about an athlete’s anaerobic-aerobic balance, a measure of their high-end aerobic power, some information about their cardiorespiratory development, and determine a sustainable training pace (i.e. their Lactate Threshold) for each cyclical modality they will employ in their training program. The following are a series of field tests that allow us to gather this information as well as some brief information regarding the interpretation of the results.

Anaerobic Speed Reserve (ASR test)

Determining the balance between an athlete’s anaerobic and aerobic contribution to high-intensity exercise is extremely valuable to coaches. It allows us to better direct an athlete’s training program to address their specific limitations in the sport. The anaerobic speed reserve test is a test that allows us to quantify the difference between an athlete’s maximal sprint speed (MSS) and their velocity at VO2max which provides us a rough idea of their anaerobic/aerobic balance. This is a useful indicator of an athlete’s current inclination toward anaerobic or aerobic metabolism at very high effort levels. The bigger the gap between their MSS and velocity at VO2max the less energy they are producing via aerobic metabolism. Athletes with larger ASR gaps tend to produce more lactate at all effort levels and therefore will fatigue faster than athletes with smaller ASR gaps.

ASR Testing Protocol (rowing)

Standardized warm-up (note: run the same warm-up protocol each time this test is administered)


Row - 3 x 10sec @ maximal effort; rest 3min b/t bouts

*record the HIGHEST /500m pace that is displayed within the 10sec window (note: this is MSS)


Rest 5min


Row - 1 x 2000m @ maximal effort

*record the average /500m pace (this is estimated velocity at VO2max), final time, and average heart-rate (note: this give you a very rough indication of heart-rate at VO2max)

To determine the ASR, you will subtract MSS from vVO2 in seconds. For example, at the TTT Regional camp Travis Mayer was able hit 1:06 /500m pace during his second effort on the 10sec MSS test. Travis also boasts an impressive 6:24 for a 2000m row (1:36 average = vVO2). Using Travis as an example we get:

vVO2 - MSS = ASR

96sec - 66sec = 30sec

So Travis’s ASR = 30sec

For reference this is the second lowest ASR that we’ve seen to date. However when interpreting these results it is also important to keep in mind their absolute scores as well. For example, an athlete who’s MSS = 90sec and vVO2 = 120sec has an ASR of 30sec (indicating balance between anaerobic-aerobic energy production) but lacks power in both systems. This is one of the advantages of utilizing a test like this, you essentially gather both relative as well as individual data in one test.

Maximal Heart Rate Step Test

Most athletes have a poor understanding of their own subjective effort and pacing levels. When we as coaches prescribe a training set at 85% there is so much room left to interpretation for the athletes that often they aren’t actually performing the work at the desired intensity level. One way to address this discrepancy during cyclical endurance training or well-designed mixed modal training is to implement the use of heart rate (HR) monitoring. The effective use of heart-rate zones requires us to know the athletes maximal HR. While there are simple equations for estimating an individual’s maximal HR there is significant individual variation. Determining maximal HR is usually accomplished by using a “step test” that forces the athlete to work at increasing intensities until failure. The highest HR elicited during the test is considered to be their maximal HR and is used to determine HR zones for future training.

Maximal Heart Rate Step Test Protocol (rowing)

*Note, in order to run this test you must first establish the athlete’s maximal effort 2000m row

This test is a bit more complicated and taxing than the previous. The test consists of progressive 4-minute work bouts (steps) in which the athlete will be required to hold a specific pace separated by 30sec rest periods. The athlete will continue increasing pace until they can no longer hold the required pace and have reached exhaustion. Heart-rate is recorded at the completion of each 4-minute window and the highest heart-rate elicited before exhaustion indicates the athlete’s maximal HR.

In order to determine the required pace for each “step” of the test we utilize the athlete’s vVO2max (average pace for 2k row). The test begins 6-steps behind their vVO2max. Each step corresponds to a change in power-output of 25W. Since wattage is rarely used to determine rowing pacing, I’ve included a “conversion chart” that will allow you to determine the pace required based on an athlete's average 2000m pace.

500m Pace to Watts conversion table, adapted from Fletcher Sport Science

Using Travis’s average 2k row pace (1:36) from the previous example, we would count 6 steps back from 1:36 (I’m using 1:35.6 from the chart) so his starting pace would be 1:51.9. Each subsequent 4min step would be rowed at the next pace on the chart until failure.

Row - 4min @ 1:51.9

Rest - 30sec

Row - 4min @ 1:48.4

Rest - 30sec

Row - 4min @ 1:45.3

Rest - 30sec

Row - 4min @ 1:42.5

Rest - 30sec

Row - 4min @ 1;40.0

Rest - 30sec

Row - 4min @ 1:37.7

Rest - 30sec

Row - 4min @ 1:35.6

Rest - 30sec

Row - 4min @ 1:33.7

continue pattern until failure

When interpreting this test I often use the athlete’s subjective feedback to give me further insight. Some athletes will be able to easily elicit a maximal heart-rate response during this test where others will reach muscular fatigue (legs) well before they are able to hit their actual max HR. In the case of the athlete limited by muscular fatigue it's usually a good indicator that they need more exposure to the modality used in the test (more rowing in this case). The max HR data gathered from this test can then be used to determine heart-rate zones for further endurance training.

Lactate Threshold Field Test

An athlete’s lactate threshold (LT) is the best physiological predictor of endurance performance. The LT usually refers to the fastest pace or highest power output an athlete can sustain without a significant rise in blood lactate. Knowing where this point is for an individual is extremely valuable. However in the absence of a gas analyzer or blood lactate meter we are left with field tests in order to estimate the pace or power-output at their lactate threshold. There have been a variety of tests created attempting to estimate lactate threshold, however the most commonly used field test is a 30min time trial. While this is relatively simple, it provides coaches with a dearth of information including pacing, heart-rate, and subjective effort levels for the athlete at their estimated lactate threshold. This data can then be used to determine training effort as well as a benchmark to track endurance adaptations throughout the course of a season.

Lactate Threshold Field Test Protocol (aka - 30min Time trial)

Standardized Warm-up


Row - 30min for max distance

*record average HR, average /500m pace, total distance

While this test is extremely simple to administer the information gathered can be implemented into training immediately. The average pace and average HR data should be used to determine pacing for all training geared toward improving an athlete’s lactate threshold. Additionally this can be compared to the vVO2max (2000m row pacing) and expressed as a percentage. For example if an athlete was able to hold 1:36 for their 2000m row and was able to hold 1:46 for their 30min time-trial you would be able to estimate that their lactate threshold pace was 90% of their vVO2max. The goal of endurance training should be to close this gap and raise this percentage as close to 100% as possible.


As this sport evolves our understanding of how to optimally train athletes has shifted with it. It is now very clear that elite athletes in this sport spend more time training at submaximal intensities than they do at all-out efforts. Up until recently this was just an observation: that the top athletes rarely left themselves flat on their backs in training. However, now that the sport is becoming more mainstream and we are starting to get some physiological data on elite athletes in the sport. Rich Froning had his VO2max tested in 2014 and it was ~69ml/kg/min (considered elite for endurance cycling/running) as well we have some recent data on Julie Foucher that indicate her lactate threshold is approximately 95% of her VO2max. In essence if she could hit a 6:30 Helen at 100% effort, she would be able to repeat 6:49 Helen’s for 30 minutes without fatiguing! Having tools to assess the endurance capacity of your athletes will be critical to creating continual progression in a sport that will only become more competitive.

~ Kyle

Created By
Kyle Ruth

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