How to Determine Your Lactate Threshold

In a previous post I discussed Lactate Threshold and how it is probably the most important training tool. Click here to read the post. So now I would love to enlighten you with how to actually determine your lactate threshold. There are several methods available and I'll list them beginning with the most effective to the least.

I. The most accurate way to measure your lactate threshold is to go to a facility offering lactate testing that measures your actual blood lactate values as you exercise at progressive intensities. This can be expensive and uncomfortable (not only are you exercising to maximal exertion, they’re periodically pricking you and taking blood samples as well). This is obviously the most accurate because they draw your blood and look at the actual mmols of lactate in the blood. They can determine when your blood lactate levels actually spike, showing your lactate threshold.

II. Another fairly accurate method that is perhaps more accessible and somewhat more comfortable is to have a Ventilatory Threshold (VT) test done. These are sometimes just called VO2max tests (because they also measure your Vo2max), but they can also determine your LT by measuring your breathing rate and the exchange of O2 and CO2. This is not quite as accurate as the lactate testing method mentioned above because the test merely predicts your LT from your VT, which tend to occur simultaneously. However, it is a much better indicator of your LT than performing field tests or just guessing.

III. If you do not have access to a blood lactate test or a VT test, then performing a field test is the way to go. As stated, it is definitely not as accurate as performing a metabolic test because it is somewhat subjective, but it can give you a good idea of where your LT is. For both tests listed below, you will need a heart rate monitor (HRM).

Field Test Method #1: 30 Minute Test

This test is basically a 30 minute time trial where you will be exercising (whether it’s running, biking, swimming, etc.) as hard as you can for 30 minutes. It is important that you do not begin too hard to ensure that you are able to finish the test. After warming up for at least 10 minutes, begin the test by hitting the start button on your HRM. If you have a HRM with a lap button, press it at 10 minutes to get your average heart rate for the last 20 minutes of the test. If you do not have a lap button on your HRM, stop and restart your HRM at 10 minutes to record the average for the last 20 minutes. Stop the test at 30 minutes. The average heart rate recorded during the last 20 minutes of the test is your possible LT.

Problems with this test arise when someone is a well-conditioned athlete and is mentally and physically able to push themselves beyond their LT for long periods of time. The average heart rate of the last 20 minutes of the test may be higher than their actual LT.

Field Test Method #2: Graded Exercise Test

This test is performed on some sort of ergometer related to your sport (treadmill for running, stationary bike or trainer for cycling, etc.) and is similar to the type of exercise test used for the metabolic tests explained above. You will need a HRM, a viewable 1-10 RPE scale, and an assistant to record values. After warming up on the equipment for at least 10 minutes, begin the test at a fairly easy pace, about a 2 on the 1-10 scale. Every minute, increase the intensity in a linear pattern (0.5-1 mph or 1% incline on the treadmill, 20-30 watts on a bike trainer). At the end of each minute, have your assistant record your RPE value and heart rate (they should be holding the heart rate receiver so you are not affected by knowing how hard your heart is working). Your assistant should also listen carefully to your breathing and record when they notice a significant increase in your breathing rate and depth of each breath, called your ventilatory threshold (VT). Continue until you are completely fatigued and can no longer continue.

To determine your LT, see if an RPE value of 7 occurs within the last five data points recorded. If it does, assume your LT is at the point where a 7 first appears. If a 7 occurs before the last five data points, but your assistant recorded your VT during the last five points, then use your VT as your LT. If neither a 7 nor your VT occurs in the last five points, assume your LT is the fifth data point from the end of the test.

IV. Probably the least accurate method of determining your LT is to take a percentage of your estimated maximum heart rate, usually suggested as 85-90% of HRmax. Whether you use 220-your age or the Karvonen (heart rate reserve) method, which somewhat takes into account your fitness level by factoring in your resting heart rate, the resulting estimated maximum heart rate may be off by as much as 25 beats per minute! Even if these formulas accurately calculated your maximum heart rate, a person’s LT may be as low or lower than 65% or as high as 95% of their HRmax, based on their fitness level. Therefore, if you were to guess your maximum heart rate and then guess your LT based upon that heart rate, the likelihood of you actually training at your true LT is slim. I do not suggest using a percentage of your HRmax to determine your LT. It would be better to simply train at a “hard” intensity, paying attention to your breathing rate and making sure you can maintain the pace for longer than 2-3 minutes but less than about 10-15 minutes depending on how fit you are.