One of the things that my coach wanted me to get done this season was some metabolic testing to determine exactly where I was at, in terms of metabolic efficiency. Endurance sports performance is very much about one's ability to use fat -- versus carbohydrates -- as an energy source. There is some debate about how best to train this, but the idea is basically that the more efficiently your body can use fat as a fuel, the faster you'll go for longer.
Note this has only a very little to do with diet and weight management, it's about how efficiently your body can run at a given pace. If your body burns more fat, that's good for body comp, but what we're talking about here is the type of fuel your system prefers at a given output. Even for a lightweight like me, your fat-based energy supply is, in athletic terms, unlimited. Not so with carbohydrates. This is the main reason you bonk out if you go too hard; you literally run out energy. So, the metabolic testing is a way to determine exactly how well your body uses fat as a fuel and how to maximize training this effect. Or something like that.
So I got set up with a local establishment to get some bike and run numbers done, on consecutive days. The test protocol is simple. They put your bike on a stationary trainer and work you against progressively harder resistance, until you hit Lactate Threshold, which is basically the point at which you're switching to anaerobic energy systems. For the run, it's the same idea but on the treadmill. You do this with a mask on that monitors the air you're breathing in and out. On the way out, it samples how much oxygen is left in the air, how much CO2 is in there, and what kind of fuel you're burning between fat and carbs. Ladies and gentlemen, the miracle of modern science.
I did the bike first. It was really pretty painless - the whole thing took about 15 minute with only the last few being particularly stressful. I made the mistake of not going to failure and instead stopped at LT; would have been good to get real VO2 Max numbers. VO2Max is the maximum amount of oxygen your body can process per kilogram of body weight. It's a general measure of how effective your cardio system is at processing air, and each person has a genetic upper-limit on this.
The next day we did the run, and this time I went closer to max. I say "closer" because at the end of the test, they had me running 8mph on a 14% incline. It's hard to go to truly max in this situation simply because the treadmill can't just stop on a dime. So if you fail or stumble, it shoots you off the back of the thing, which is embarrassing, at best. But I got pretty close.
So how did all of this turn out? And what does it tell me? Well...
Well it turns out my bike and run situations are pretty different. Of all the data produced, I thought these graphs were the most telling (bike and run, respectively):
So what you're looking at here is a graph showing the ratio of fat calories to total calories that I'm burning at a given heart rate. Now, I've been doing a big running focus lately, but the differences are pretty astounding. Notice the huge drop off on the first graph at 131 bpm - I go from 60% usage right down to 35%. That's not good.
On the run - the lower graph - I get 50%+ usage all the way into zone 3. Moreover, if you look at the actual numbers in the lower left, I'm burning almost as much fat in Z4 on the run as in Z1 on the bike. What does this mean? It means my run base is in good shape. The bike, not so much. That's something I'll be working on for sure.
This matches up with another general idea of your Aerobic Baseline (marked as AB in the graphs above). The closer you can work your AB over towards your threshold (which doesn't move much), the better shape you're in. Again, bike vs run. Pretty big difference. Note how much closer together the lines are on the right.
Finally there was the VO2 Max data. This is more of a novelty item than a fully useful number. VO2 Max is mostly determined by genetics. A high VO2 max is a good performance predictor, but it's not the whole equation. I had a V02Max test in my teens and came out near 70, which is really on the higher end. But I wasn't all that good at bike racing, relatively, so I kind of dismissed it.
I mentioned that I didn't go to max on the bike. Even so, I hit a number of 67.2, with a "predicted" max of 87. Okay, I know that number was silly. 87 is Lance Armstrong stuff. No way. But it wasn't too far off; the next day I came back and hit 77 on the run at pretty close to a max effort. It's not 87 but it's still up there, see chart below. I'm not entirely sure how they decide what's "average", but a fitter person will hit a higher V02 max. So I think the numbers below are taken from the overall population regardless of their fitness. What I'd like to see is a graph that has just some subset of "fit" people, by whatever measure.
So what does all of this mean? The above means that I can't continue to claim that I'm low-on-talent with a straight face. Clearly, my performances don't line up with the VO2 max predictors above, something I'm reminded of every time I compete. And that's OK, but clearly I'm missing, or still developing, some important piece of the puzzle there. In any case, the guy doing the test said that's one of the higher numbers he's seen in a while. Again, this number isn't terribly useful for what I'm doing, it's just interesting. Yay me.
Anyway, the usual purpose of these tests is to help dial on your heart rate "zones" so you can be confident you are maximizing your training effect. The top two graphs have that Zone data, which the vertical colored bands corresponding to the heart rates at the bottom.
One thing that's clear as day: there is lab data and there is real-world data. The lab showed my threshold on the run at 176bpm on the heart rate. Which is just ridiculous. At 176 on the run I'm starting to get tunnel vision and I'm lucky if I can hang there for 10 minutes. Looking at the actual numbers, the lab testing shows my Z2 range to be 144-152. Zone 2 is where a lot of work gets done, but my sense is that 150 is tempo for me. It doesn't feel like endurance work. What's more is that I recently laid down a pretty hard-to-argue-with threshold number at the Seattle Half of 162. That's a 90 minute effort, so it should be just below, but pretty close to threshold.
The training zones, at least on the run, just don't make much sense to me. And maybe that's OK given where I'm at with my running and how my progression has been. From where I'm at now, I feel pretty confident about what it's going to take to continue to improve my running, and my performances have been pretty good relative to my history and training there. I'll just stick with it what I'm doing.
On the other hand, the bike zones look reasonable from my experience, although they're lower than I would have expected. What's more is that the fat usage graph is extremely telling and matches up well with the limiters I've experienced on the bike and even go so far as explaining some performance issues I've seen there. So clearly I need to improve my fat usage on the bike, and if those numbers are to be believed it means that basically I've been doing way to much bike work at 140 bpm, which is pushing Z3 for me right now. That uses too many carbs and I don't get the right training effect. That's what the guy running the test said, that's what my coach says, and I think that's what Gordo would say. But I'll admit I'm still having trouble embracing that, and I think a lot of it is my ego not wanting to go out and ride my bike that slowly for the next few months. It's far easier to cling to the idea that getting faster simply requires going harder.
However, it's worth noting that I didn't do any real speed work on my running between April of 2006 and November of 2007. At least 95% of my running was done at low heart rates and average pace numbers that were usually around 8:45-9:00 per mile. The increase in run volume and frequency that I did later this year in my winter running focus caused me to start running faster within just a few weeks, and adding a small amount of tempo work to that regimen resulted in even more gains and durability. And even since then I have done very little work that most runners would consider as real speed work - for me it just means running for 30-60 minutes of a 90 minute run at 155bpm or so, which is still sub-threshold. And I've only done a couple of those. So, I suppose one could argue that's been a more effective training protocol and that mimicking it on the bike would lead to improved fat usage and, therefore, improved performance.
That's basically the best way that I can think of to evaluate the usefulness of this testing, for me. It's weird for me to say that I trust one set of numbers when the other set are so clearly out-of-whack. But given that the bike data lines up with my perception of my limiters, I'm willing to lend it some credence. For most people, I'm not sure that I can really recommend spending the money on something like this. If you're embarking on an Ironman training process, you've got a high level of commitment and investment already so it's easy to justify this as another tool in your planning process. If you're just trying to get in shape or "just finish" an event, I think there are plenty of easy and free field tests you can do that will get you most of this data and have it be "close enough".