Lactate threshold (LT) is a valuable measure for working out your endurance capabilities and deciding on proper exercise intensity to achieve your goals.
First lets get the science lesson out of the way.
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 uses oxygen for energy, to anaerobic metabolism. The latter does not require oxygen and creates energy through the combustion of carbohydrates.
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At this crossing point, your body starts to generate lactic acid which is further broken down into a compound called lactate. Lactate accumulation in the muscles serves as a temporary source of energy, which actually delays fatigue because it keeps you going a little bit longer. But not much. When lactate production exceeds its clearance rate, it accumulates in your body causing increased acidity in your tissues that contributes to feelings of fatigue.
For experienced runners LT typically occurs at 90% of maximum heart rate. For average runners, the value is well below 90%.
When exercising at or below your LT any lactate produced by the muscles is removed by the body without it building up. As explained above, your body primarily uses oxygen for energy production. When you are above the LT, lactate starts to accumulate resulting in rapid deterioration in performance resulting from fatigue, nausea and more. Put simply, runners that are above their lactate threshold will experience burning sensations in their muscles that will slow down and eventually halt athletic activity.
So with the science lesson out of the way, it becomes a bit clearer what LT actually represents. Its essentially the highest workload at which the body is able to achieve a steady-state condition. It is the highest performance intensity that can be tolerated for relatively long periods of exercise (~race pace). Over the LT the body is unable to remove lactic acid and re-use it quickly enough.
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. Its good to do both types of workouts as each has its own health and performance benefits.
Knowing your LT can help customize your workouts as its a useful measure for deciding proper intensity for training and racing. The actual value varies between individuals and can be increased 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.
The good news is, it is now easier than ever to work out your LT thanks to wearable technology. There are a number of devices that will do the work for you by tapping into Firstbeat analytics to provide you with the necessary calculations. This includes the Garmin Forerunner 935, Fenix 5, Forerunner 630 and Quatix 5.
Obtaining a value requires a stable Vo2max estimate and enough quality heartbeat data recorded across a range of different intensities. Or you could opt for a guided test designed specifically to record the data needed to detect your LT. You will also need to wear a heart rate chest strap along with your smartwatch.
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.” The goal is typically to raise the heart rate when this occurs.
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.
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