Finger-sticks, Ear-pricks; I’ve done them all.
From weekend warriors to elite cyclists (and at times myself), I’ve used blood lactate measurements to help understand an athlete’s metabolism and ultimately to make more personalized recommendations to improve their training and performance.
Lactate, a byproduct of metabolism, is always circulating in the body. As the body relies more on anaerobic metabolism, the lactate concentration we can measure begins to rise. For an in-depth understanding of lactate metabolism and shuttling, see Episode 281 of Fast Talk.
Lactate samples are taken from capillary blood, often via a fingertip or earlobe. Today, these are usually measured with a single drop of blood tested in a handheld device. Earlier in my career, I was quite adept at collecting samples in glass capillary tubes and testing on a medical-grade “bench-top” analyzer. The stories of packing this 40-pound machine into my luggage and flying to a team camp in California are best told over a beer (or the Fast Talk Podcast).
While lactate data can be useful for training, it has limitations that prevent its widespread use: samples are difficult to collect, and they only represent discrete instances in time.
Enter the highly anticipated continuous lactate monitor (CLM). The internet (and peloton) has been abuzz with anticipation of this new technology. Some, myself included, have publicly speculated that CLMs will be game changers, but I’m here to question if that’s the case.
How continuous lactate monitors work
Based on continuous glucose monitors with sensors tuned to lactate instead of glucose, we can begin looking at the pitfalls of such a device. These devices work by inserting a very thin needle that lies in the thickness of your skin, sampling the interstitial fluid between your cells. This fluid has many of the same components of blood—minus the blood cells and much of the protein. This means that glucose and lactate do exist in this space and are able to be measured.
The continuous monitors are constantly “sipping” from the interstitial fluid and measure concentrations by recording electrical changes as the substance in question (e.g., glucose or lactate) interacts with specialized enzymes in the device.
RELATED: The Endurance Athlete’s Guide to VO2max and Lactate Tests
While this measurement technique can produce accurate results (similar to how the medical-grade YSI 2300 I packed into my luggage tests lactate and glucose) it does induce a known lag time. When sampling capillary blood in a traditional lactate test, we are testing blood that is circulating the body in mere seconds. Therefore, the concentration of blood lactate near the working muscle is functionally equivalent to that in your fingertip.
However, the process of lactate diffusing out of the bloodstream and into the interstitial space is highly variable. This diffusion is based on local concentrations of lactate, local blood flow to the sensor placement area, and even hydration status—as dehydration discourages movement out of the circulatory system. Because of this, continuous glucose monitors are known to have a roughly 20-minute delay in their reporting, and we can assume similar for continuous lactate monitors based on the same technology.
This is the crux of the situation because when we’re making training or pacing decisions on the fly, we need information that accurately reflects our current state. For perspective, athletes complain about the lag in heart rate vs. power/pace, and that is roughly 30 to 60 seconds, not 20 minutes!
RELATED: Understanding the Norwegian Training Method
Pros
- Constant—not discrete—measures of an important metabolite
- Relatively unobtrusive
Cons
- They will be expensive
- The delay may make the data worthless
Should you use continuous lactate monitors?
Now, all of this is pure speculation. Deep in my heart, I hope these issues are solved (with more than a predictive algorithm). However, I’ll be waiting until devices are validated in peer-reviewed research before buying, and then I’ll likely check (and double-check) by pricking my own finger until I can trust it. If that happens, continuous lactate monitors will be a game changer!
