What is Lactate Threshold

Lactate threshold is a term than is commonly used in training vernacular, but has most runners more confused than a high school kid in calculus class. I’m not going to lie, the complexities of lactate threshold, or lactate and lactic acid, can be a bit daunting for the beginner runner. However, if we break things down very simply and avoid discussion of the more scientific terms, it can be easily understood to the point where you can appreciate its application to your training.

What is lactate or lactic acid?

Lactate, or lactic acid as it is commonly known, gets a bad rap thanks to some faulty science from the 1970’s. While lactic acid contributes to why we hurt at the end of races, lactate is actually a source of energy. Your body breaks down glucose for energy and a by-product of this process is lactate. During easy running, your body reconverts and recycles this lactic acid back into energy and efficiently expels the waste products. Therefore, the production of lactate will remain relatively constant while running at an easy aerobic pace, which doesn’t require a huge demand for energy.

As you continue to run faster and demand more energy, the production of lactic acid will slowly increase. At some point, whether it be too fast a pace or holding a steady pace for too long, the production of lactic acid will soar and your body will no longer be able to convert lactate back into energy and expel the waste products. This point is commonly referred to as your lactate threshold. The lactic acid then floods into system, muscle power is diminished and you begin to slow down (1). Ultimately, lactic acid is one of the largest contributors to why you slow down as the race goes on.

Concisely stated, what is your lactate threshold?

So, in short, your lactate threshold is defined as the fastest pace you can run without generating more lactic acid than your body can utilize and reconvert back into energy. This pace usually corresponds to 10 mile or half marathon race pace. Therefore a tempo run or threshold run is basically a workout that is designed to have you running at just below or at your threshold pace.

But why is this important?

By running just below your lactate threshold you can begin to decrease (or improve, depending on how you look at it) the pace at which you begin to produce too much lactic acid for your body to manage.

For example, at the beginning of a training plan for the marathon, your threshold might be 10 minutes per mile. This would mean you could run a 10 mile or half marathon race at this pace. As you do more tempo runs, your body gets stronger, adapts to the increased production of lactic acid, and decreases this threshold pace to 9:30 per mile.  Now, since your threshold is lower, you are able to run faster with less effort, which for the marathon means you can burn fuel more efficiently – saving it for the crucial last 10k.

In my opinion, lactate threshold is usually the most glaring weakness in runners I begin working with. It’s not an easy training term to understand and it takes a lot of control and effort to keep tempo runs in the lactate threshold range. Plus, busting out 400 meter or mile repeats is a lot more fun – that comment is for us sick runner types who love coming home dripping sweat from a tough workout and love nothing more than to sit on the coach eating freeze pops. However, development of your lactate threshold can be one of the easiest ways to improve your running, both short-term and long-term.

(1) The actual cause of the fatigue is caused by the hydrogen ions interfering with energy production. The decreased muscle power occurs because calcium, an electrolyte needed to help muscles contract, is unable to make its way to the muscles. This is more complicated stuff for the science lovers out there, but suffice it to say that excess lactic acid causes the fatigue in a roundabout way.