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All About Lactate Threshold
Written by Dr. SkibaI get a lot of e-mail’s from athletes and coaches alike regarding lactate threshold (LT). This month’s column is going to focus upon lactate, how and why it is made, and what LT means as a practical matter regarding your training.
For many years, it was thought that lactate was a waste product generated by exercising at an intensity where the need for oxygen outstripped the body’s ability to deliver it. Because there was not enough oxygen, the reasoning went, the cells of the body needed to generate energy through alternative pathways that resulted in lactate production. The original experiments that led to this conclusion were not particularly elegant, and if memory serves involved a bell jar, and the repetitive electrical stimulation of half a frog who had met his untimely demise at the hands of some grad student.
If there is one thing I can get through to you in this article, let it be this: Lactate production does not equal lack of oxygen. This is an old wife’s tale, brought about by the ritual sacrifice of unfortunate amphibians and reinforced by uneducated Internet chatter.
So now, the explanation…
As it turns out, your body has several ways of generating ATP, which is the universal energy currency of the body. One way to think about it is in terms of currency exchange. You may come back to Heathrow from holiday with a pocket full of U.S. Dollars (fat) and Euros (carbohydrates), but if you want to catch a cab home you are going to have to convert them to Pounds Sterling (ATP).
So, to make this ATP, your body has to burn both carbohydrates and fat. It is always and without fail burning both. The fuel mixture is determined by the work load. It goes something like this. You go out for an easy jog, and your cells are burning fat and carbohydrates. Since you are not working very hard, your cells are able to meet most of the energy demand by burning fat. You are also burning a little carbohydrate, and the end product of this is something called pyruvate. The pyruvate gets processed to make energy as well.
So, you are cruising along on your jog and some of your buddies catch up with you. They are doing an interval workout, and you want to keep up with them, so you start running harder. Soon, you come to a point where you can’t meet the energy demands with fat burning alone. You need to start burning more carbohydrates. The problem now is that your cells are so busy that they cannot process all the pyruvate you are making. It starts to build up, and is converted into lactate, which is transported out of the cell. The lactate really isn’t a waste product, but rather a high energy compound that is transported to the liver, kidneys, brain, and heart to produce more energy there. Rather than trash, think of is as recyclable. Note that as all of this is happening, there is plenty of oxygen around. You are not “anaerobic”. You are simply experiencing the effects of a necessary change in fuel balance.
So, what is lactate threshold? Lactate threshold is the point where you are making enough lactate that your blood level increases by 1 mmol over baseline. Great, but the question you should be asking yourself is, “Why do I care?’
This is easy. Below LT, your exercise capacity and time to fatigue are much greater than above LT. Once you go above LT, you are significantly tapping into your limited carbohydrate storage capacity. Once you run out of carbohydrates, you will “bonk”. Remember, you only carry about 2000 calories worth of carbohydrates onboard. However, you carry many tens of thousands of calories worth of fat onboard, even if you are very skinny. Thus, in long distance racing, it is to your advantage to try and not venture too far beyond LT, and to drink/eat in order to keep up with the amount of carbs you are burning.
Now, are there ways of determining LT? Yes, and they involve poking you with something sharp and collecting blood during an exercise test of some kind. No fun. However, it is possible to figure out something closely related, called the Maximial Lactate Steady State (MLSS). Simply put, MLSS is the point where lactate production equals lactate elimination. It happens at an exercise intensity just a little bit higher than LT. Testing for your MLSS is easy…go out on your bike, hammer as hard as you can for an hour, and record your average power output. There you go. For running, go out and kill yourself for a distance greater than about 10k, and perhaps closer to an hour. Your MLSS will be closely related to the pace you can maintain.
This is powerful information. Once you know this pace or power output, you know the point at which you need to back off during the race. For instance, if you know that you can only last an hour at 300 watts, you know that your Ironman bike leg should be done at much less than this wattage, since you are going to be out there for 5-7 hours. If you are racing a 40k TT, you know that your target wattage needs to be about 300 watts…any higher, and you may bonk and end up crawling to the finish line. You can also re-test during the season to monitor fitness. If you started out at 300 watts for an hour in February, and can maintain 330 watts for an hour in April, it is safe to say that you are fitter, and can now train harder.
As always, feel free to e-mail with any questions, and remember to keep training your brain. It is the fastest way to get faster.
