I recently read the book 80/20 Running by Matt Fitzgerald, which makes the case for doing 80% of training at low intensity and only 20% at moderate/high intensity. I’ve been making the mistake of running too hard on every run, increasing my chance of overtraining and injury! But if I hold back and go easier on some runs, how do I know whether I’m going too easy or too hard? I know the answer is in using my heart rate monitor (dusting the cobwebs off as we speak), but where to set the heart rate training zones?
That’s where metabolic stress testing, or more commonly known as VO2 max testing in exercise circles, comes in. I found somewhere local where this test is done in a doctor’s office, and so in my case it was covered by insurance.
This blog post gives an excellent description of how the test is conducted. Basically, you’re hooked up to a bunch of wires while on a treadmill or your bike mounted on a trainer. The workload is increased in increments until you can’t take it anymore. All the while you have a plastic piece in your mouth to measure your oxygen consumption during the whole process. Although I would have been more comfortable doing it on the bike, I opted to do it on the treadmill because the results can be a bit different for cycling versus running.
Here’s my rough approximation of what a typical graph of oxygen consumption over time looks like.
Then target heart rate training zones are set based on recommended percentages of VO2max. This is generally considered more accurate than the default way of taking percentages of maximum heart rate.
However, there were two anomalies with my test. First, my oxygen consumption rose, then decreased, then rose again! This was not an issue with the test equipment, as I also felt a “second wind” during the testing. The technician said this was uncommon but not unprecedented. I’m not sure why this happened, maybe I needed more of a warmup before the intensity was increased?
Second, I gave up after only 7 mph at a 4% grade, which is equivalent to 7:34/mi pace outdoors. (Yes, there are conversion tables for this!) My most recent 5K of 23:41, which is a 7:40/mi pace, suggests that I could have gone on for longer. I don’t have much treadmill experience, so I must have been freaked out by the prospect of going all out to the point of tripping and falling.
That made it somewhat challenging to come up with recommendations. First was the recommended paces, which were generated from the Jack Daniels’ (the coach, not the beverage) Running Calculator from my recent 5K race time. I found an iPhone app which can generate the paces, here’s a screenshot.
Wow, I already knew that 1:45-1:50 for 400m intervals was about right for me, so nice to see an independent confirmation!
The heart rates for each zone were determined as follows. They line up pretty well with the Jack Daniels recommendations based on percentage of maximum heart rate.
- Easy: 118-144
- Marathon: 147-164
- Threshold: 161-167
- Intervals: 174-182
- Repetition: N/A (since max is 182)
My heart rate at my anaerobic threshold is 172. If I assume that is the heart rate at my lactate threshold, then per the 80/20 Running book, the heart rate zones can be calculated as a percentage of lactate threshold can be calculated. The results come out similar.
The next day I found somewhere flat and ran the paces above with my heart rate monitor, with the following results:
- Easy: 10:00/mi, 142
- Moderate: 8:42/mi, 155
- Threshold: 8:08/mi, 164
They came out pretty close, although the easy run was at the high end of the heart rate range. And I didn’t bother to check my heart rate for the Interval and Repetition paces – lap time is recommended instead, as the durations are too short to make up for the cardiac lag.
Now it’s time to close out the year with mostly easy runs (and spend some time on the bike too) while I figure out my plans for the new year!