Lactate Testing for Runners

Recently I had a lactate test done for the first time. Even after so long in this sport, the results were fascinating and surprising. This article shares what the test involved, my results, what I learned, and how I am going to change my training.

For those newer to this topic or interested in going deeper, I also recommend checking out Uphill Athlete’s website and articles on lactate and lactate threshold testing.

my lactate test protocol

My test was conducted on a treadmill at the GW University lab. After taking resting lactate, I did an easy 15 minute warmup beginning at 8:45 minute per mile pace. Every 3 minutes, a finger prick lactate sample was taken and pace was increased steadily to around 7:45 min / mile by the end of the warm-up.

After the warm up, the treadmill was set to a 1% incline with pace at 7:30. The remainder of the test was 5 minute intervals with pace increasing each interval by ~15 seconds per mile until failure. I tapped out at 6:00 min / mile some 40 minutes later.

My test results

Below is a graph of my lactate levels vs. HR. My first lactate threshold (LT1) is around 160bpm, where lactate crosses 2 mMol / L, which is the top of my aerobic zone or Z2. The second lactate threshold (LT2) is sometimes defined as when you cross 4 mMol / L, which was in the high 170s. However, when combining various data sources including Rate of Perceived Exertion, the lab estimated my LT2 to be 172 bpm.

These results indicate I am highly aerobically efficient, which isn’t surprising after 15+ years of high-volume aerobic training but was nice to confirm. Strong aerobic fitness is shown by the curve remaining flat as heart rate increases. With less aerobic fitness and efficiency, the curve will steadily increase at lower heart rates, and some athletes may not be able to go below 2mMol / L at all. My curve stayed flat for a very long time, to the point where the lab techs started getting worried and double testing my levels!

The gap between LT1 and LT2 is another indicator of aerobic fitness, with less than a 10% gap indicating aerobic efficiency. My LT1 and LT2 were 7% apart.

what did i learn?

I was shocked at how high my heart rate was at both LT1 and LT2. Prior to the test, I guessed LT1 would be around 145 and LT2 around 165. Getting to LT1, crossing 160 bpm, is hard work for me and takes me well below 7 min miles on relatively flat terrain. Crossing LT2 is extremely difficult and generally happens only when I’m fresh and doing something like hard hill intervals.

LT1 and LT2 were 88% and 94% of max heart rate, respectively. These are high ratios, again indicating aerobic fitness but also suggesting there are fewer aerobic fitness gains to be had than I would have expected.

what am i going to do differently?

First, I would benefit from more high intensity work, such as Vo2Max intervals. With fewer aerobic fitness and efficiency gains available, raising the ceiling is the best way to improve. I did this test after 6+ weeks with no high intensity work given Hellgate, end of season recovery, and easing back into training. Given that, it isn’t surprising that high intensity work is needed and beneficial. I am always stronger on the aerobic / slow twitch side vs. anaerobic / fast twitch, so this is a good reminder to stay focused on the high intensity work. I will benefit more from short, fast intervals versus longer intervals or tempo runs.

Second, the vast majority of my aerobic, easy running is in Z1. While I do get into Z3 / Z4 during hard workouts, I rarely go above 145 and into Z2 on easy or aerobic runs. Previously, I thought that 145-155 was in the dreaded “grey” zone that should be avoided.

With high training volume (~800 hours a year for me), significant Z1 work is a good thing. As fitness increases, Z2 can become stressful on your body even though you are staying aerobic. Kilian’s data showed 58% of Z1 volume with around 20% in Z2, which makes sense given his extreme fitness and training volume.

I am far less than 20% Z2 and believe I would benefit from more. However, I will need to be cautious with the biomechanical stress of Z2 and make sure I avoid overuse and injury. Especially on flatter terrain, Z2 creates significant stress for me. I will try adding more Z2 running during one easy run each week, keeping the rest primarily Z1. As training volume increases, I will also add Z2 uphill workouts during treadmill doubles, which is a great way to get to higher heart rate without adding much stress on the body.

I hope to repeat the test in 2-3 months when I am in peak season and have been doing more high intensity training. I am fascinated to see what, if anything, changes and will report back. If you want to learn more about lactate threshold testing, structured training, or coaching, please do reach out at willtoruncoaching@gmail.com.