Tuesday, October 23, 2007

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

1 comment:

Chris Whyte said...

Alan, how are your determing AeT? In your first on interpreting lactate curves you say the following:

"Let’s begin by looking at the first point, what we are terming the aerobic threshold or VT1.
The point best correlated to Ironman performance among the curves is the first point, i.e. speed at AeT."

But in this article VT1 is considered lactate threshold.

Thanks, Chris