What's Cool In Road Cycling

Feel The Burn: Just What Is Lactate Threshold?

If there is one stat that every cyclist wants to know, it’s their “VO2max.” Just what does this secret number mean? And more importantly, why is it a pretty near meaningless red herring, and what number do you really want to know? PCN sport scientist Stephen Cheung gives us a primer on the lactate threshold and how to use it to plan your training…

Most times when athletes want me to do some fitness testing on them, they tell me they want to know their VO2max. However, as seen in Figure 1, the problem with VO2max is that it is mainly genetic and doesn’t really change with training once you are relatively fit, so it’s not that valuable a marker of the fine-tuning of fitness that athletes want. It also corresponds to a workload that you can handle for only a very brief period of time, maybe about 5 min. Therefore, it doesn’t really have too much race application.


Figure 1.

MAX INTENSITY
What you really should be interested in is the maximal intensity (speed, wattage or heart rate) that you can sustain without blowing up from building up too much lactic acid or lactate. Since this effort is pretty much the pace that you can sustain during critical race situations such as time trials or breakaways, this is the most important marker of training that you want to base your training around and to improve. If your heart and cardiovascular system cannot supply enough oxygen to your working muscles to generate energy using aerobic (“with oxygen”) metabolism, then your body is forced to rely on the anaerobic (“without oxygen”) metabolism. One byproduct of this is lactic acid, which is what causes the severe burning in your muscles that eventually forces you to slow down or stop.

OVER THE THRESHOLD
If you ever want to get a bunch of exercise physiology geeks like myself into a bar brawl, one sure-fire way is to ask us to define this threshold. Since I’m sitting here alone and in the safety of my own lab, I’ll give you my own definitions and let the gods be damned. In Figure 2 (below), “Lactate Threshold” or LT is the exercise intensity at which you’re starting to produce more lactic acid than you can get rid of. “Onset of Blood Lactate Accumulation” or OBLA is the intensity at which your lactic acid reaches a value of 4 mmol, which is generally the level most people can tolerate for about a 30 min TT without blowing up.


Figure 2.

Going back to Figure 1 again, we see that LT is also much more sensitive to training for already fit athletes than VO2max. Look at it another way. If me and my evil twin Skippy had the exact same VO2max of 50 mL but I can pedal at 90% of it (45 mL) and Skippy can only pedal at 70% (35 mL), chances are that I’m going to be a stronger cyclist than him.

To me, the lactate threshold makes it a much better marker to base your training around than VO2max or maximum heart rate. One of my main tasks with cyclists therefore is to determine the heart rate or power at LT and then work to increase it. The best way to do it is by spending interval time right near the LT. This generally corresponds to 85-110% of the power output at LT, or 95-105% of the heart rate at LT. As I discussed before when talking about interval physiology (see related article on interval physiology), you should begin by doing more intervals at the lower range of these intensities to build in the quantity of training, then increase the quality by increasing the duration and/or intensity of the intervals.

Finally, you need to retest your lactate threshold regularly in order to adjust your training zones as your fitness improves. If you can’t afford to get the test done professionally, another option is to set up your indoor test lab (see related article on Test Labs At Home) and then ride a 10 k TT. The heart rate or power will be pretty close to your actual lactate threshold values.
Have fun tickling your lactate threshold and keep the questions coming!

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About Stephen:
Stephen Cheung is an Associate Professor of Kinesiology at Dalhousie University in Halifax, Nova Scotia, Canada, with a research specialty in the effects of thermal stress on human physiology and performance. He has been an avid roadie since beginning university in the mid-eighties, and still has non-indexed downtube shifters on his winter bike and wool jerseys hanging in his closet. He can be reached for advice or comments at [email protected]

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