In celebration of a positive annual 2012 physical, I decided to do a follow-up VO2 max test with POTENTRx in Seattle. The test today went great, and I learned lots of new things about my personal fitness, and fitness in general, just as I always do during these tests. I’d love to share some of what I learned here, as anyone who cross-trains, does triathlons, or otherwise participates in more than one sport will likely be interested by some of what I learned today.

I decided that since I’ve been cycling a fair amount lately, I’d like to get a baseline VO2 max on a stationary bike, as opposed to a test on an elliptical trainer like I did back in July 2011, when I got a dismal result of 24.9. I’ve posted previously about those results, what I’ve been doing with the data, and my positive results to date, so if you haven’t already read that post, I recommend doing so first and then coming back to finish reading this one.

I scheduled my test today with the always affable and extremely knowledgeable Sean Machak at POTENTRx. In addition to being a fitness uber-expert, Sean’s also a car guy (he owns a tuned Subaru STi), so of course we get along. I assumed that my results from this cycling VO2 max test would be easily compared to those from my earlier elliptical test, but Sean warned that wouldn’t quite be the case. The actual VO2 max value might translate fine, but the resulting heart rate training zones would likely be different. more on that later. Still, after discussing it over with Sean, I decided that I wanted cycling results, and so that’s the test I did. The results were encouraging, as well as enlightening.

To help follow along, I’ve uploaded the analysis of my test results here. I’d suggest keeping them in a new browser window so you can follow along as I go through it.

The first item of note is my new VO2 max value: 32.4. That’s a massive step up from 24.9 less than a year ago, and I was stoked to see that my data-driven training over the past many months has been working (dropping 30+ lbs was also a dead giveaway, but the more data the better). This also correlated with the 33 that my Polar FT80 heart monitor calculated based on resting heart rate over time. So it’s nice to know I can always do a quick and dirty VO2 max test (kinda) any time I want.

The next line down on the report shows my aerobic threshold: the point at which my body is optimally oxidizing fat calories per minute. This section also shows my anaerobic threshold (sometimes called the lactate threshold) which is where my body burns no fat, pulls energy only from blood sugar, and starts to build up lactic acid faster than my body is able to recycle it.

To help understand these thresholds better, here’s a helpful chart I stole from Wikipedia showing graduated exercise thresholds:

Back on my report, I had mistakenly thought that the specific heart rate zones shown there would be universal across all exercises I perform… but I learned today that they’re not! In fact, the farther an exercise is anatomically from walking (which is the primary activity our bodies are designed and/or have naturally evolved and adapted to perform), the higher the physical effort required to perform that exercise. An elliptical trainer, for example, is extremely similar to walking, and so my body does it easier than running, cycling, or swimming… each of which is progressively and inherently more physically demanding than walking. This blew my mind, but after talking it over with Sean, it made total sense. Our bodies simply have to work harder to do things they weren’t designed to do naturally, but the more we do them the more adapted to those activities we become.

This means that the heart rate zones derived from this test are useful to me only while on a bicycle, and that in order to get specific updated zones for elliptical workouts, I’d need an updated test on an elliptical. That’s fine, since the tests are only $180 and worth EVERY penny to me. In fact, POTENTRx gave me a 10% discount as a repeat offender, so my test today was actually $162. A bargain for this kind of insight.

So basically, according to these results, I need to keep my heart rate at 126 BPM while on a bike to get the most efficient fat burning (2.1 calories per minute, according to the report). If I take that up to between 129-139 BPM, my fat oxidation rate drops to only 1.1 calories per minute, and when I get to the 140-146 range, I’m not burning any fat at all. Yes, I’m still burning calories (from blood sugar), but not fat calories – and that’s still my primary fitness goal for the time being.

On an elliptical, however, my test results from last year showed that 131 was my ideal fat burning heart rate, and it’s safe to assume that number’s probably gone up a bit since my last test because of my training. But to isolate the exact number and target zones, I’m going back in to POTENTRx to do a VO2 max elliptical test in a couple of weeks. For now, I’m still writing this post at 131 BPM on my elliptical, because I know I’m burning fat at that heart rate.

So it’s possible (and in fact, this report showed it’s actual) that my body can perform one mode of physical activity at one given heart rate, and a different (less adapted/more difficult) mode at a somewhat lower heart rate, but that the two activities at the two different rates could have the same cardiovascular effect and physical demand on my body! So a 123-128 heart rate on a bike is the “same” aerobically to my body as, let’s say, a 133-138 heart rate on an elliptical… because I’m less adapted to biking.

An article shared with me by Sean at POTENTRx explains further explains this concept:

Maximal heart rate (HRmax) is generally reported to be slightly (~5%) higher when obtained from an incremental treadmill test as compared with an incremental cycle test in untrained subjects. In addition, the relationship between HR and exercise intensity or VO2 is exercise dependent and is influenced by
training mode, postural position or laboratory
environment. In triathletes, the HRmax observed in cycling is often lower by 6–10 beats/min than that obtained during running. Longitudinal investigations have demonstrated HRmax to remain relatively stable over the course of a season, with higher values (~5 beats/min) observed in running than in cycling. (Physiological Differences Between Cycling and Running – Millet, Vleck, Bentley, Sports Med 2009)

I’ve updated my Polar heart rate monitor with the new zones from this report, and padded them a bit to encompass both my cycling and elliptical fat burning and cardio zones. I’ll just need to be vigilant to make sure I’m in the right zone on the right equipment. And after updating my elliptical test in a couple of weeks, I’ll know exactly what I should be doing in different exercise modalities to keep getting positive results.

Again, the adage generally attributed to Socrates of “Know Thyself” applies in the 21st century just as it did in 400 BC. So don’t exercise blindly. You may luck into results, but chances are you’re expending effort sub-optimally, and could get better results with less effort by simply knowing your body and exercising in the appropriate zones.

And if you live in the Seattle area and want to get your own VO2 max test performed, feel free to name drop me at POTENRx, and ask the receptionist to schedule you with Sean. I’d love to hear about your results!

I also love blog comments, so please feel free to leave yours below.

P.S. Click here to see the cardio workout I performed while writing this post!