A new study reveals that athletes can find their lactate threshold heart rate by feel.
Any good training plan for runners includes workouts that are intended to be performed at “lactate threshold” intensity. What is the lactate threshold? It is the intensity of exercise at which lactate—an intermediate product of carbohydrate metabolism in the muscles—begins to accumulate in the muscles because it’s being produced faster than the muscles can use it and the excess “leaks” into the bloodstream.
Why does every coach in the universe want runners to train at lactate threshold (LT) intensity once a week or so? Because training at LT is a powerful and efficient way to build fitness. For most runners the lactate threshold corresponds to the fastest pace that can be sustained for 30 to 60 minutes (closer to 30 minutes for less fit individuals, closer to 60 minutes for highly fit individuals). So it’s not a super-high intensity, but it’s not a low intensity either. It’s somewhere in the middle—call it moderately high. As such, it is hard enough to stimulate big gains in fitness but not so hard that it leaves a runner wiped out, as long as it is done in judicious amounts.
The greatest benefit of LT training is that it greatly increases a runner’s capacity to sustain faster running paces for prolonged periods of time. It doesn’t make you faster, but it does make you much slower to fatigue when running fast. Since LT intensity is in the neighborhood of 10K and half-marathon race pace for most runners, we’re talking about a type of training that significantly increases how long a runner can sustain a desired race pace for such events.
The lactate threshold is defined by a concentration of lactate in the blood—specifically, a concentration of 4 millimoles per liter. But runners don’t care about that. They care about the heart rate or pace that is associated with that particular lactate concentration. If they know either of these values then they can train at lactate threshold intensity on their own by monitoring their heart rate or pace. Heart rate is a little more useful than pace because it is relevant to all environments, whereas the pace that is associated with LT varies depending on whether you’re running uphill, downhill, or on level terrain.
The traditional method of determining LT heart rate is a lactate threshold test conducted in an exercise laboratory. After warming up on a treadmill you run at incrementally increasing speeds while wearing a heart rate monitor. For example, you might start with 3 minutes at 6.5 mph, then do 3 minutes at 6.7 mph, and so on. At each speed a blood sample is taken from a fingertip and its lactate concentration is measured. You keep going until you’re running at a pace that produces a blood lactate concentration that exceeds 4 mmol/L. The results are graphed and used to plot the exact heart rate at which that special threshold concentration was reached.
The problem with lab-based LT testing is that it’s expensive, inconvenient, and invasive. To spare athletes from these negatives some coaches have come up with field tests to determine lactate threshold heart rate. One such field test is a 30-minute time trial. You warm up and then run as far as you can in 30 minutes. Your average heart rate in the last 10 minutes is your estimated LT heart rate. A comparison of this procedure to the lab-based LT test found that it was quite accurate. But it has a downside too: It’s very stressful—the equivalent of running a 30-minute race.
Isn’t there some accurate way to determine LT heart rate in the field that does not leave a runner hyperventilating at the end? There is now. Johannes Scherr and colleagues at Munich Technical University recently demonstrated that runners and cyclists can find their own lactate threshold by feel—or, more precisely, by perceived exertion.
Perceived exertion is a global, subjective perception of how hard an exercise effort feels at any given moment. Scientists have traditionally used a tool called the Borg Scale to quantify perceived effort. The scale ranges from 6 to 20, which seems weird, but it was originally intended to correlate with heart rate values of 60 to 200 (which it doesn’t really do very well in practice anyway). On this scale, a perceived exertion rating (or RPE) of 6 represents a laughably easy effort and a rating of 20 represents an effort that is so miserably hard that exhaustion is but moments away.
Over a long period of time Dr. Scherr and his collaborators performed cycling and running LT tests on 2,560 men and women between the ages of 17 and 44 years. Except there was a twist: Instead of taking objective measurements only, as in conventional LT testing, they also asked the subjects to rate their perceived exertion on Borg’s 6-20 scale at each step. When the researchers crunched the numbers they discovered that a subjective effort rating of 13 on this scale consistently correlated with a blood lactate concentration of 4 mmol/L. This was true across ages, genders, exercise modalities and fitness levels.
The practical implication of this finding is that runners like you can now find their own LT heart rate at home without undo suffering. All you have to do is strap on a heart rate monitor and perform your own graded exercise test. Start off at a low intensity and rate the effort on a 6-20 scale. After 2 or 3 minutes, increase your speed slightly and rate your effort again. Keep doing this until your RPE reach 13 and then note your heart rate. That’s your lactate threshold heart rate.
Personally, I am particularly gratified by Johannes Scherr’s study because it validates my own perceived exertion-based lactate threshold field test that I designed for PEAR Sports last year. This one is even easier to do because it uses a less unwieldy 1-10 scale (LT falls at 6 on this scale) and I guide users through it step by step with audio instructions delivered through headphones. When I did the test myself I got an LT heart rate of 160 bpm. When I went to a lab for a formal LT test a few days later the result was 159 bmp. Not too shabby!
About The Author:
Matt Fitzgerald is the author of numerous books, including Iron War: Dave Scott, Mark Allen & The Greatest Race Ever Run (VeloPress, 2011). He is also a Training Intelligence Specialist for PEAR Sports. To learn more about Matt visit www.mattfitzgerald.org.