One of the best measures of running fitness is lactate threshold (LT), which is the running speed or heart rate at which lactate—an intermediate product of aerobic metabolism in the muscles—begins to accumulate rapidly in the bloodstream. If your training program is working, two things are sure to happen. One is that you will run faster at the point where your blood lactate level spikes. The other is that your heart rate at this threshold will increase (i.e., your lactate threshold heart rate will move closer to your maximum heart rate).
In addition to being useful as a measure of running fitness, lactate threshold is also useful for establishing individual intensity zones for training. That’s because LT happens to fall at a moderate intensity level. Efforts that are more than a little faster than the pace or heart rate that corresponds to LT are defined as high intensity and offer a different set of benefits than moderate-intensity training. Efforts that are more than a little slower than the pace or heart rate that corresponds to LT count as low intensity and offer yet another set of benefits.
Establishing individual target intensity zones to use in your training requires that you know the running pace and/or heart rate that corresponds to your lactate threshold. Exercise scientists determine lactate threshold in a laboratory environment. In a typical LT test, a runner starts running at a low speed on a treadmill and is then required to run incrementally faster until the point of failure. At each step, the person leading the test takes a small blood sample from the runner’s fingertips and measures its blood lactate concentration.
After the test is completed, the collected data is used to create a graph in which the blood lactate concentration is plotted against pace and/or heart rate. Lactate threshold is pinpointed where the blood lactate concentration begins to increase rapidly. In a typical trained athlete, that point corresponds to roughly 85 percent of maximum heart rate and falls somewhere between 10K and half-marathon race pace.
The protocol just described has some obvious disadvantages. It requires special equipment and expert assistance, it’s relatively costly, and it’s invasive. For all of these reasons, it can’t easily be done with optimal frequency (once every six to eight weeks) by most runners. Fortunately, there are do-it-yourself alternatives to lab-based lactate threshold testing that work quite well. Let’s take a look at three of them.
The Time-Trial Method
The time-trial method of determining lactate threshold pace and heart rate can be done on a treadmill set at a 1 percent grade, on a running track, or on any other flat, smooth surface that’s conducive to fast running. It also requires some means of measuring time elapsed and distance covered as well as heart rate. Be sure to conduct this test on a day when you are not fatigued from recent hard training.
Begin with several minutes of easy jogging to warm up. When you’re ready, start tracking time, distance, and pace on your treadmill or watch and run for 30 minutes at the fastest pace you can sustain for that amount of time. Be careful to avoid the common mistake of starting too fast and then slowing down toward the end of the time trial due to fatigue, which will produce an inaccurate result. When you get to 10 minutes, note your heart rate.
At 30 minutes, stop and note your heart rate again. Calculate the sum of your heart rate at 10 minutes and your heart rate at 30 minutes and divide by two. That’s your LT heart rate. Your LT pace is your average pace for the entire 30-minute effort, assuming your pace was fairly steady.
A 2005 study by scientists at East Carolina University found that this method of determining LT heart rate and pace is very accurate. Its downside is that it’s hard—equivalent to running a half-hour race.
The Race Time Method
We know that a runner’s lactate threshold pace is a strong predictor of his or her race times. But it also works the other way around: Your race times can be used to estimate your pace at lactate threshold.
I often use coach Greg McMillan’s Running Calculator for this purpose. Simply enter a recent race time in the relevant field and press the “Submit” button. Near the top of the results page, you will see “vLT” with some numbers next to it. That is your approximate lactate threshold pace.
To determine your LT heat rate, warm up and then accelerate to your LT pace on a flat, smooth surface. Wait for your heart rate to plateau and note it. That number is your LT heat rate.
The High-Tech Method
A new option for do-it-yourself lactate threshold has emerged recently. It entails using LED lights to noninvasively read the concentration of lactate in the blood. The sensor is contained in a sleeve worn around the calf. A smartphone app guides the runner through a traditional LT test workout protocol (i.e., starting at a slow pace and accelerating every few minutes until exhaustion). When the workout is complete, the app uses the data collected from the sensor to calculate lactate threshold pace and heart rate as well as appropriate training zones.
A 2015 study published in the Journal of Strength and Conditioning Research reported that this new method exhibited a high degree of accuracy when compared against the laboratory method. In my own testing, I found that the LED light method closely matched the result that I got from the race time method.
What’s Your Lactate Threshold?
Do you know your lactate threshold pace and heart rate? You should. Fortunately, getting accurate measurements without expert help (or blood!) has never been easier. Choose your preferred DIY method and start tracking your fitness and training more effectively today.