VO2 testing for Long Course Triathletes

Alan Couzens, MS (Sports Science), CSCS, PES

Part II: Case Studies

In the short time since I wrote the first post on VO2 testing, we have done a substantial number of tests on athletes of a wide range of abilities. I will present some of the (anonymous) data here to provide you with some concrete ideas on the levels of pure power and substrate efficiency required for different performance levels and hopefully to provide you with the impetus to plan a trip to Boulder to get tested and see how you stack up!

First, let me present the curves (enlarge in 'paint' to view) and then I will chat about some of the distinguishing features that we have observed between these athletes of differing abilities.

Case Study 1: ~9:00 Ironman (not Gordo J)

Case Study 2: 10:50 Ironman

Case Study 3: 12:20 Ironman

* Fat Burning
Careful observation of the curves will show that the big differences lie in the blue shaded area. In short, based on the athletes we have seen, the faster the guy, the more fat they burn at and around AeT and the longer they keep burning fat. In the case of the 9hr guy pictured, he has a peak fat oxidation rate of ~8kcal/min and holds a fat oxidation rate of ~5kcal/min all the way up to VT1 (or ~Half Ironman efforts). This pattern has been consistent across all of the faster guys that we have tested so far and is supported by the literature, e.g. Jeukendrup et al. (1997), who found fat oxidation rates of 5.6kcal/min in trained cyclists (mean VO2max = 67ml/kg/min) vs. 3.4kcal/min in untrained college males (mean VO2max = 48ml/kg/min) while pedalling at ~60% VO2max.

*Aerobic Threshold (AeT):
According to Martin (1997), AeT values range from 35-60% of VO2max, with better trained athletes falling higher on the scale. For our 3 subjects, relative AeT values were 61%, 48% and 60% of VO2max resp., In absolute terms, this represented 175, 152 and 200 watts. At first glance, this would seem to favour athlete C over athlete B over an Ironman duration race. However, in real terms, athlete C’s poor substrate economy at this pace means that, for him, AeT power is a poor predictor of Ironman performance.

When I pull the data from the 3 athletes above, the point that best correlates with their actual Ironman intensity is a point of ~10kcal of CHO oxidation on the substrate curve. For athlete A, this is 74% of VO2 max (240 watts). For athlete B, this is 71% of VO2max (202 watts) and for athlete C, this is 59% of VO2max (175 watts). This makes logical sense, since Ironman is fundamentally an exercise of carbohydrate sparing. Additionally, it makes mathematical sense when we look at the substrate shift over long duration exercise:

If we assume a peak glycogen storage of ~2000kcal in muscle stores and a maximal exogenous CHO oxidation rate of 4kcal, an endogenous CHO oxidation rate of 6kcal/min would only last 5hrs 33minutes. At first glance, it appears that even at these relatively low levels of intensity, the Ironman is a metabolic impossibility. However, studies by Costill, (1970) and Bosch et al (1993) along with test on our own resident guinea pig, Gordo Byrn, have shown typical RER changes of 0.1 or more as we get 2hrs+ into metabolic testing and substrate shifts of 30% or more towards contribution from fat. This means that for a well trained athlete, we would expect CHO oxidation to almost half as they get 2hrs or more into the race. In practical terms, this means that our 5hrs 33mins demolition time, could almost double to 11hrs, and for a decent athlete becomes within the realm of possibility for an Ironman distance. As this calculation (and his race heart rate data) suggest, this 10kcal/min point isn’t going to work for a 12+hr Ironman.


*VT1 (“Lactate Threshold”)
At least in our very limited sample, VT1 as a % of VO2max appears to be a better correlated to Ironman performance than AeT as a % of VO2max and it makes good intuitive sense. An athlete with a high VT1 is able to use the more economical FOG fibers at higher workloads before recruiting the glycogen guzzling Fast Glycolytic Fibers (Coyle, 1984).

VT1 values for elite athletes vary between 74-83% of VO2max (Padilla et al, 1999). Athlete 3 may have some room for improvement here, but in relative terms, he is still not too far behind the other guys (or outside normative values) in this measure of performance.

One other interesting observation, when we look at the VT1 point is the breakdown in substrates at that point. For all athletes, VT1 represents the point where there is a rapid drop off in fat burning and a rapid increase in CHO utilization. However, a trend that we are witnessing for our better athletes is an ability to hold their fat oxidation rates pretty well up to this point. This may represent a potential area of improvement for our 10:50 guy.

*VT2 (“Functional Threshold”/ "OBLA”)
A very trainable adaptation. Elite values are typically 80-90% of VO2max, while values for the general population are typically 40-50% VO2max (Martin et al, 1986, Padilla et al., 1999)

Again, all of our athletes do well in this respect. There appears to be a trend that the faster athletes have the higher VT2. However, all athletes are within elite parameters for VT2, yet only one of our athletes would be considered elite from an Ironman perspective.

We could be onto something interesting with these differences in fat oxidative capacity, especially at likely race intensities. I will keep updating as we learn more.

References available upon request.

For further information on discovering your own personal limiters via testing at our Boulder Sports Performance Lab, contact me at alan@endurancecorner.com

VO2 testing for Long Course Triathletes

Part I: Setting Accurate Training Zones

Alan Couzens, MS (Sports Science), CSCS, PES

As many of you know, Mat, Gordo and I have recently opened a small human performance lab in Boulder. It has been a very interesting experience on many fronts. As a guy who is totally obsessed with numbers, I have been quite surprised at the reaction of a number of quite elite local triathletes when we approached them about testing. The prevailing attitude about VO2max testing still appears to be that VO2max is the ‘end all, be all’ when it comes to endurance athletics. In fact, many athletes are so afraid of discovering what their number (and by extension of logic, their athletic ceiling) is that they have declined the opportunity to get tested and get some very useful information about their current physiological limiters that they can then apply to their training. The VO2max number is just one (and probably the most useless) metric that we obtain from a VO2 test. It is not particularly relevant to ultra-distance athletes, whose VO2 numbers are often quite pedestrian when compared to their short-course counterparts, and, at the risk of offending my fellow exercise scientists out there, to suggest that we only have a maximal 15-20% upside to improving our VO2 max is quite simply bollocks. Even taking body composition and economy improvements into account, I have witnessed numerous clients exhibit improvements in both lab measures and ‘real world numbers’ far in excess of 20%. There is a definite plateau in the stroke volume/oxygen delivery side of the equation. However, the aVO2 side of things, while much slower to improve, is a multi-YEAR adaptation.

But let me dismount from my VO2 high horse for a moment, as I explain some of the other (non-maximal) VO2 metrics that can provide you, as an athlete, with some very useful information on your training zones, your true physiological strengths and weaknesses and where you should best direct your training efforts for the coming year.

Training Zones
VO2 testing is a particularly useful way to determine training zones. It provides the coach and athlete with some additional measures that heart rate and lactate testing do not provide. It also makes the ‘no-mans land’ area between zones easy to identify and eliminate, thus maximizing the desired training effect.

Critical points on the VO2 curves:

Zero Net Energy Utilization (NEU)
The curve immediately below displays the total work being produced at each respective intensity level, along with the relative contributions from fat and carbohydrate for one of our athletes.




As a very fit athlete, this guy has reached a point where he is able to train at an intensity where he can accumulate work with no net glycogen cost. I.e. he is able to replenish glycogen at the same rate at which he is using it. Several studies have shown that the maximal rate of replenishment under conditions of exercise is approximately 3kcal of Carbohydrate per minute (Jeukendrup and Jentjens, 2000). This threshold is indicated by the horizontal line on the graph. If the athlete can work out at an intensity in which they produce less than ~3kcal minute of work from Carbohydrate metabolism, they are in essence not dipping into their glycogen stores. For the athlete in the figure above, you can see that he accomplishes this. The point where the curve rises above the line corresponded with an intensity of 62% of this athlete’s VO2max. In other words, this athlete can exercise at 62% of their VO2max without inhibiting glycogen recovery from their harder sessions. This is a critical ability because it significantly increases the total amount of work that can be accumulated in a training week. In volume overload periods, this can take the form of training camps or, in the context of the basic week, the athlete at this level can employ low intensity aerobic training while they are recovering from key sessions.

Maximal Level of Fat Oxidation
From VO2 data, we can also determine a specific training intensity that elicits the greatest absolute contribution from fat oxidation. For the Ironman athlete, this is the key adaptation and, in my experience, is the greatest predictor of Ironman success. Frequently, an athlete who is relatively fast in short course racing will be disappointed when they attempt to transition to long course. The reason is simple, long course racing has very different limiters to short course racing. Consider the data below from 2 actual athletes:

One of these athletes has a 9:54 Ironman to his credit. The other is yet to break 13:00. Of course, I wouldn’t be going through all of this building of the suspense if the results were as expected. You guessed it, the 9:54 guy has a VO2max of 41 ml.kg.min. So, what data is missing?

The key data missing is economy & fat oxidation rates. At Athlete B’s “Steady” pace, he is able to produce 5.5kcal/min from fat oxidation. Athlete A is topped out at 4.3 kcal/min. Now, before Athlete B’s ego gets too inflated, it is worth noting that Dr Tim Noakes, in his book Lore of Running, postulates that Mark Allen must have generated 10.5 kcal/min from fat (!) in order to run a 2:40 marathon at the end of an Ironman. He also points out that this value is 50% greater than the highest level that he had recorded in elite 10K and marathon runners in his South African human performance lab. Clearly, it is an understatement to say that this ability deserves a good amount of attention (& training time) for the Ironman athlete, especially considering the ‘upside’ that most of us have in this area.

Ventilatory Threshold 1
A VO2 test is useful not only to monitor this ability, but also to determine the appropriate zones to use to improve it. If you take another look at the chart, you will see that from 50-75% VO2max, there is a good chunk of energy contribution coming from fat oxidation. However, once the athlete goes a tick over 75%, the energy coming from fat oxidation disappears rapidly. oxidation. It is very useful, as an Ironman athlete to be able to pinpoint this spot in setting your training zones. There are many ways to approximate this, e.g. the Maffetone method etc, but it is worth noting that, in my experience, there is more individual variation here than even with maximal heart rate and the best way to see that important breakpoint at the cellular level is with individual VO2 testing.

Ventilatory Threshold 2/"Lactate Threshold"
On a VE curve, you will typically see 2 clear deflection points, where VE and VCO2 both increase in a non-linear fashion, i.e. there is a jump in Ventilation (the blue line) and VCO2 (the purple line) that is noticeably greater than the preceding steps. The first of these (VT1 on the curve below) is related to the metabolic shift from fat to carbohydrate oxidation noted above (McLellan and Skinner, 1980). The second of these is caused by the rapid accumulation of lactate in the blood once the athlete passes the lactate balance point and the consequent rise in ventilation elicited in an effort to expel the additional CO2 created from the dissociation of lactate. On a normal individual, this point (VT2) will correspond exactly with LT2, or the onset of blood lactate accumulation (OBLA).



This value is also of use to us as athletes because it represents another distinct limiter to the amount of volume that we can tolerate in a training session and over the course of a week. Even small excursions above the VT2 line correspond with a very high recovery cost (due to the shift in fibers used) and for the long course athlete very little performance benefit.

VO2max
Of course, the final point of interest is the point of VO2 max, which, coincidentally, corresponds with the max value of the VO2 curve (providing this point fulfils certain criteria). For the long course athlete, the VO2max has very limited predictive value, &, consequently demands limited attention to its improvement. Even a 2:40 marathon requires only a VO2 of 53ml/kg/min. For most well trained individuals, this maximal value is not going to be limiting. Going back to our Athlete B, despite his relatively low maximal value, he was able to run 3:22 for an Ironman Marathon (67% of his VO2max). This value corresponds with Dr. Noakes’ estimates for Mark Allen’s optimal Ironman marathon (i.e. 66% VO2max) IMHO, until you are approaching these relative values, a focus on raising your maximal value is not appropriate.

In part II, I will get more into the nitty gritty of actual values for different athletes and the consequent training implications.

If you are interested in having a VO2 test performed and interpreted by our team, drop me a line at alan@endurancecorner.com