Image source: Garmin

Sports watches & lactate threshold, stamina training for runners

Lactate threshold (LT) is a valuable measure for working out your endurance capabilities and deciding on proper exercise intensity to achieve your goals.

First let’s get the science lesson out of the way. It’s not really too difficult to understand.

Lactic acid serves as a “backup” energy source for your body. During very intense exercise, your circulatory system cannot keep up with your muscles’ demand for oxygen. This is when muscles shift from aerobic metabolism, which predominantly uses oxygen for energy, to anaerobic metabolism. The latter creates energy through the combustion of carbohydrates. It’s at this point that your body needs more energy than can be provided by simply breathing in oxygen.

A byproduct of burning carbohydrates is lactic acid which your body further breaks down into a compound called lactate. Lactate accumulation in the muscles serves as a temporary source of energy. It delays fatigue and keeps you going a little bit longer. But not much.

Essential reading: Aerobic and anaerobic training with wearables, what you should know

Your body can get use up lactate only so fast. When lactate production exceeds its clearance rate, it quickly accumulates causing increased acidity in tissues that contributes to feelings of fatigue, nausea and more. Put simply, runners that are above their lactate threshold will eventually start to experience burning sensations in their muscles fairly quickly. This will slow them down and eventually halt their athletic activity.

For well trained athletes LT typically occurs at around 90% of their maximum heart rate. For average runners, the value is typically below this figure. That’s the bad news. The good news is that professional athletes are least likely to improve their LT. Your chances are better.

Wearables and lactate threshold, stamina training for runnersSo with the science lesson out of the way, it becomes a bit clearer what LT actually represents. It’s essentially the highest workload at which the body is able to achieve a steady-state condition. Or the highest performance intensity that can be tolerated for relatively long periods of exercise. Go over your LT for a while and your body will be unable to remove lactic acid and re-use it quickly enough. You’ll start to slow down.

Think marathon running. Given you have put in the time and effort to train, you will probably be able to go the distance provided you remain below your LT for the bulk of the race. Go too quickly and you will be looking for a bench to sit down in the middle of the race.

This also helps to explain the difference between aerobic and anaerobic training. The first is exercise that can be performed at a sustained rate for long periods and that uses oxygen for energy production. The second can only be done in short bursts as it causes you to be quickly out of breath. It’s good to do both types of workouts as each has its own health and performance benefits.

LT appears as a heart rate value and a pace value. Knowing these figures can help customize your workouts as its a useful measure for deciding proper intensity for training and racing. As mentioned, the actual value varies between individuals and can be improved with regular exercise. This is because exercise leads to adaptations in skeletal muscle which prevent lactate levels from rising. Your body also becomes more efficient at using oxygen for energy.

It is now easier than ever to work out your LT thanks to wearable technology. And no, you don’t need to visits an exercise lab and pay for costly tests.

A number of sports watches will do this for you by tapping into Firstbeat analytics to provide you with the necessary calculations. This includes (but is not limited to) the Garmin Forerunner 245/245M, Forerunner 945 and 935, Fenix 6, (5 Plus, 5 and 3) range, Forerunner 645 Music, Forerunner 630, Forerunner 735XT, Quatix 5, Tactix range and MARQ collection.

Obtaining a value requires a stable Vo2Max estimate and enough quality heartbeat data recorded across a range of different intensities. This means you’ll need to wear a heart rate chest strap along with your smartwatch in order to get the calculations, as they require HRV data (the variations in beets between your heart beats). This can be done automatically during normal running, or by opting for a guided test designed specifically to record the data needed.

According to Firstbeat and as shown in the chart above, “your LT is detected by isolating deflections in your heart rate variability that correlate to key indications of how your respiration patterns respond to the intensity of your activity.”

An interesting option, as suggested by one of our readers, is to use a muscle oxygen sensor such as Humon Hex or Moxy. These are wearables that actually measure the oxygen in your muscles. Our review of the first of these can be found on this link.

Hex dishes out real-time audio and visual feedback that helps you understand the limits of your body. It does this by measuring the hemoglobin saturation in the quadriceps. There’s also a guided test for determining LT by using a treadmill or a stationary bike and it takes about a half an hour to complete.

The final option of course is to use an estimate of 85%-90% of your maximum heart rate as your LT value. Some suggest the alternative of taking the average pace of somewhere between your best 10K and half-marathon race pace.

If you are a runner knowing your LT helps personalize your training. It provides you with the tools necessary to set the proper pace for workouts, tweak your heart rate zones for more effective training, and keep tabs on your existing endurance limits. It can also improve your race times on the all important day.

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Marko Maslakovic

Marko founded Gadgets & Wearables in 2014, having worked for more than 15 years in the City of London’s financial district. Since then, he has led the company’s charge to become a leading information source on health and fitness gadgets and wearables.

One thought on “Sports watches & lactate threshold, stamina training for runners

  • Be more accurate with a muscle oxygen sensor like Humon or Moxy.


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