My Lactic Threshold Test Results (Feb, '09)

A few weeks ago, I spent the morning with the Stanford Human Performance Lab (HPL) to do some lactic threshold testing and get a benchmark for the early stages of the training year. Although I'm usually not a "train by the numbers" guy, I thought it would be good to figure out if I'm at least in the ballpark with my target heart rate ranges. Exercise Physiologist Phil Cutti was my guide and task master.

Phil first had me lay down on the "Dex" machine (a Lunar iDXA DAX System made by GE Healthcare) which used low level x-rays to get a full body scan of my body fat levels. It took about 10 minutes of sitting still for it to spit out an x-ray image of me with some disturbing numbers. Sixteen percent body fat? That's 4-5% higher than last year at this same stage! It's the nightly ice cream, I know it! Damn, I seriously need to shed some pounds.

(The "Dex")

Not so fast, said Phil. The Dex is extremely accurate in measuring body fat, including areas that aren't usually measured with a caliper test, such as fat around your intestines and in your muscles. In short, it's not fair to compare the results of the Dex with a caliper test. We then had a good discussion about what is the best target body fat % given my age, target race of 100 miles, the risks of dieting while training, and the potential to turn all this fun training into a five month hunger-driven grumpfest. Phil emphasized that overall fitness should be the goal, not a certain weight target, and I certainly shouldn't push to the point of risking getting sick or I would never make it to the starting line. He also pointed out that my weight - 156 lbs - was only 3-4 lbs higher than my "race weight" from last year. In short, my normal training schedule will probably get me down to 150-152 lbs and it may not be worth stressing to get any lower.

The Dex readout also had a lot of other information, although it wasn't clear how to use it for training purposes. For example, I'm carrying more lean muscle mass and fat on my left side, which might indicate asymmetry in my stride or leg length. My BMI is in the normal range. My android (fat above the waist level) to gynoid (fat below the waist level) ratio was 0.86, indicating less risk of cornary disease. Hmm, good to know, I guess.

From there, Phil led me to the world's most insane treadmill (it goes to 20 mph, just in case Usain Bolt drops by) and explained the process for the lactic threshold test. I would run 6 minute intervals starting at 7mph; normally this is done in 4 minute increments, but since my target race was ultra-distance he thought it best to lengthen the interval. After each interval I would step off the treadmill so he could take a small blood sample from my ear lobe, and then he would increase the speed 0.5mph and I would do it again. While I ran, he would measure the lactic acid content of my blood, as well as ask me what my perceived effort was. We would continue this until I couldn't complete a six minute interval or indicated I was ready to stop.

It began slowly, which gave me a chance to get to know Phil a bit better. For many years he was an elite cyclist until he broke his back in an accident. He has since made a long and amazing recovery, and even completed the North Face 50k last year. His passion for understanding the body's ability to perform and heal were contagious. I didn't even mind that he was making me bleed every few minutes. ;-)

(The tools of the trade - a Lactate Pro blood monitor and HRM strap)

For about 90 minutes, I pounded away on the treadmill until I finally said going beyond a 5 min mile pace would risk me projectile vomiting all over their clean lab. In retrospect, I probably should have eaten breakfast sooner in the day. ;-) After a quick warm down, he sat me down with the results. First he shared an analogy of the body to a machine that helped frame the discussion. It went something like this:

Chassis (what you're dealt with) -> Body shape and size
Engine (ability to process) -> VO2Max and Lactate Threshold
Horsepower (how fast/hard) -> Pace/Power Output
Miles Per Gallon (how long on the same energy) -> Running Economy

So there are many things to consider when training, and this test was specifically focused on the engine. We spoke about how I am currently in an aerobic phase of training, so I haven't been pushing to the red line at all and that should be taken into account.

(The blue line is my heart rate at each speed, the red is my lactate concentration)

He showed me the chart, and we talked about how the goal of training is to push the red curve down and to the right by specifically addressing two areas - aerobic training to increase my speed at the same lactic levels, and LT/speed training to improve my overall lactic threshold. The results indicated the following training ranges:

Aerobic - 131 to 151 bpm (roughly 8-9 mph on a treadmill)
Threshold - 151 to 164 bpm (roughly 9-10 mph on a treadmill)

I noticed two things right away. First, my current aerobic training zones (125 to 140 bpm) and pace were too low. After speaking with Phil about how I had gotten those ranges from a VO2 Max test two years ago, he basically said it was likely I was improving both my aerobic capacity and running economy over that time period. But he also emphasized that it's good to have some long runs where I stay on the low end of the aerobic range to help train my body to process fat. Second, my current threshold training zones (162 to 170 bpm) were too high. So basically I needed to go a bit harder in aerobic training, and could go slower on my harder runs and get a similar benefit.

Phil spent 20 minutes with me to explain how these aren't hard and fast rules since there are other benefits of training beyond these ranges. For example, a hard track workout may exceed the threshold heart range, but give tremendous benefit to running economy and turnover (my "miles per gallon"). He also had lots of other little tidbits, and was careful to explain how his recommendations for me are different than what he would tell a 20-year-old on the track team because (a) my ability to adapt and recover are different, and (b) the ultra distance has a very different set of needs than a 5k/10k.

Phil was generous with his time to answer all my questions about training levels, recovery, calorie intake, stride efficiency, and how to adopt these track-based learnings to the ever-changing trail courses. We agreed I would come back again in a few months to get another checkpoint and dial in my target HR and speeds for Western States.

I felt energized to train with all this new knowledge, and the clarity of knowing there are some things I can affect by sticking to a plan. It may be worth the $200 just for the boost of morale! Now back to the trails...

- SD