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My parents-in-law gave me a great gift for the holiday season this year - a gift certificate for a full VO2 Max and resting metabolism test. Last week I went to BaySport of Redwood City, CA, where Physical Therapist Brian Tomason put me through two sessions of testing to find out how my body utilized oxygen, fat, and calories. Both sessions used a system by New Leaf which tracked my oxygen and CO2 usage through a mask, and my heart rate. Brian doesn't get many ultrarunners, so he was excited to see what my "abnormally high levels of racing" might yield.

I've never really done much benchmarking of my heart rate (HR) zones prior to this, aside from the standard "220 beats minus your age" kind of thing. 90% of my runs are really for fun, loosely organized around a "long fartlek" or "go until it hurts". But now that Sophie is around, I've felt the need to make my ever-disappearing training time as efficient as possible. I figured a good starting point would be to make sure my training HR zones are correct. I know can hold 158 beats/minute through a 10k and it feels hard, so I figured that was roughly what my anaerobic threshold (AT) was (AT is when you start building lactic acid, and you're burning almost all energy from glycogen instead of fat - read: unsustainable for long periods of time). I do most of my aerobic training between 130 and 145 beats/minute, which feels easy to me, but just enough where I can feel my breathing pick up.

The VO2 Max Test
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The first test was the V02 Max test. For this, they strapped on the mask and an HR monitor, and put me on a treadmill. Over the course of 25 minutes, they slowly cranked up the speed and incline until I maxed out at 12 degrees and 10 miles/hour (and nearly passed out). This calculated the oxygen and CO2 levels at each heart rate. Brian used other systems to find my body fat %, etc. Here are the test results:

MaX HR: 172. I guess that's not bad. It sure felt like the "max"!

VO2 Max: 73.3. The VO2 Max represents your peak oxygen uptake, ie, your ability to deliver oxygen to your muscles. Brian said that anything over 60 is considered "above average shape", and that most people come in around 40. A professional athlete that is tapered would come in around 80-90. Overall, it looks like my body is utilizing oxygen well, but there may be some room to grow.

Calorie Burn in Aerobic Zone: 13.1 kCal/minute from fat. Brian said this is a very high rate for use of fat calories, but he's not surprised given the volume of training and racing. Basically, I've tuned my body to burn fat very efficiently when I'm at an aerobic pace.

Anaerobic Threshold: 125 beats/minute. This is the point where your body starts needing to use glycogen instead of fat to process calories. I was very surprised to see how low this was, particularly given that I have run 50-milers with an average heart rate of 145 beats/minute. If this test was right, I haven't been doing any true aerobic training since my heart rate is too high on my "easy" runs. Close examination of the output chart shows that I am very efficient at burning fat below 110 beats/minute, but it drops off like a cliff between 110 and 140 beats/minute. A better trained athlete would have this holding steady of decreasing gradually to an AT much closer to my Max HR.

The Resting Metabolism Rate Test
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The next morning, I came in for a resting metabolism test to determine what my caloric burn needs are at rest. I had fasted for 12 hours, and they strapped the mask on me again and had me chill out in a dark room for 20 minutes to relax as much as possible. That is, as much as one can with a big tube strapped across your mouth. ;-)

The results of this test were also very interesting:

Resting heart rate: 38 beats/minute. Most of the men in my family have a low heart rate and I'm fairly well conditioned, so I'm not surprised this is low. I know individuals with resting heart rates as low as 32-34 beats/minute.

Resting metabolism caloric burn: 516 calories. This means that I only need 516 calories per day to maintain my body weight, or 744 calories on a typical non-workout day. What?!? That's like two donuts!!! A typical BMI would say that 2200 calories is about right for my age, and a standard chart prediction for a trained athlete would have been closer to 1700 calories. Brian was a bit baffled at the low reading, but then pointed out that nearly all of those calories were consumed from fat and both my oxygen and CO2 levels were shallow. Basically, my body is insanely efficient at rest. Apparently I could fast for a week on the couch and only lose one pound.

Recommendations
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Brian said that I'm basically in really good shape, and that the post-test recommendations are mostly for people trying to get in shape, not crazy endurance people like ultrarunners. But he did say this:

1) My body fat level is just fine. Given my ability to stick to high levels of training, he said I could certainly get down to the 9-10% found in most elite 10k runners (ab cover shoot, anyone?). But when he saw the 100k's and 100-miler on the schedule combined with my fat-burning aerobic capacity, he suggested it would be good to carry an extra couple of pounds for fuel. He also warned that since my resting metabolism is so low, it's hard to lose weight via diet, and the only outlet would be to exercise even more than I already do.

2) I should consider "aerobic intervals" to raise my AT. Brian was a bit perplexed by my low AT calculation (given my race pace at previous 50-milers, which would have had my bonked or dead by mile 30), and warned that the test could have been off. But the quick drop off from aerobic to anaerobic indicates that I could benefit from much slower workouts just under my AT. He suggested going 5 minutes just under AT, resting for 15 seconds, then repeating over an hour.

3) I should do more weight training. Brian congratulated me on being efficient with what I have - by his calculations, my body is very good at using every muscle and every gram of fat. But that means I'm "always at 11", requiring me to recruit all that I have for every race. Weight training could give me more muscle mass, and require me to recruit less muscles for the same amount of work. I certainly have enough headroom in my resting metabolism to feed a few more muscles.

I'm going to take Brian's advice on a few fronts, and do more weight training and at least one weekly aerobic interval. I did one aerobic run this weekend at 120 beats/minute, and it was excrutiatingly slow. But there could be benefit, so I'll stick with it. I don't want to turn my favorite daily activity into too much work, so I'm going to stick with "fun" for most runs.

It certainly is helpful to have some specific numbers associated with calorie burn during exercise, and a more realistic benchmark for my daily intake. I'm burning much more during exercise than I had thought, but am using much less outside of exercise. All of this data will be helpful in charting out a food/race plan for longer runs.

I'm open to feedback if any of you have (a) ever done anything like this, and (b) see anything crazy in my test results or recommendations.

Thanks, SD

PS - Congrats to all the racers who mastered the Woodside 50k this Sat!