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What is Lactic Acid?
Lactic acid, more correctly termed lactate, is a product from burning glucose anaerobically (without the direct use of oxygen) for energy. Contrary to popular belief, our bodies are always breaking down glucose anaerobically to some degree, and thus producing lactate. Even as you read this, you’re producing a small bit of lactate.

Typically, our bodies produce high amounts of lactate when the intensity of exercise increases or as we begin to fatigue. The reason for this increase is because our anaerobic metabolism begins to take up more of the slack and provide more energy for the body – and in turn produce more lactate. Our anaerobic metabolism is a lot less efficient than our aerobic metabolism, but it happens to produce energy much more quickly – which is why it becomes useful during high intensity states.

Our faster-twitch muscle fibers are naturally more anaerobically strong than our slower-twitch fibers, so exercise which involves more of these faster fibers tend to also produce more lactate.

How is lactate relevant to training?
Though lactate itself isn’t bad – it doesn’t cause stiffness, burning or soreness – it is indeed a marker of fatigue. Thus, when lactate production is high and greater than your body’s ability to clear it, there is usually a correlating level of fatigue.

From a training standpoint; your easy days would want to have lower lactate levels – as you would want to avoid excessive fatigue or using fast-twitch fibers for prolonged periods. However, on your session days you may want to train around or above your lactate threshold – indicating harder metabolic stress (the demand for energy) on your body.

As an athlete you may want to strive to have a high ‘lactate threshold’, which would mean that you can sustain a relatively high level of effort before lactate begins to accumulate exponentially. This would indicate an ability to run at a relatively high intensity before reaching the point where you start becoming less metabolically efficient and begin generating a high amount of fatigue. Typically, the further above the threshold you are, the shorter the amount of time you have left until you’re unable to continue at the same level of output.

Some runners (particularly middle-distance runners) would want to be able to have a high level of ‘lactate tolerance’. The nature of these events will require the athlete to run at an intensity where they are inevitably producing a high amount of fatigue and fatigue-associated products like hydrogen ions, which increases your blood acidity. These athletes would therefore want to train in order to tolerate the specific fatigue they’re dealing with on race day.

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