All About Thresholds...
If you've been involved in the sport of triathlon for more than a few weeks, you've probably heard people talk about various thresholds .... lactate thresholds, anaerobic thresholds, aerobic thresholds. You've maybe heard another load of weird stuff: critical power, VO2max and my personal favorite .... the fat oxidation threshold.
The question that's on your lips is, "what are these things?" And, the more important thing is "should I care?"
I'll answer the first question last .... and I'll tell you that the answer to the second question is "definitely maybe."
The best description of a threshold I can come up with is "a non-linear change in response." Pretty tech-y eh?
In order to understand this let's go back to the 17th century and the work of Robert Hooke. When Bob wasn't fighting Isaac Newton, he found the time to come up with Hooke's Law .... which is all about springs. Hooke's Law basically states that the extension of a spring is proportional to the applied load i.e. if you hang a 1lb weight on a spring and it extends by one inch then, when you hang a 2lb weight, it'll extend by two inches. And so on.
Easy so far ....
The problem is, Hooke's Law is only true to a point. You might get to the stage when you hang 20lb on the spring but, it extends by 22 inches not the 20 inches you were expecting. Furthermore, when you take the weight off, it doesn't return to it's original length and, if you then put 22lb on the spring, it breaks!
This, my friends, is a non-linear response! You have reached a threshold: in this case, the threshold is the yield point of the material.
This is equally a good analogy of lactate threshold: it's the point at which your body's response as evidenced by your heart rate is no longer proportional to the applied load, the "speed" at which you are swimming, biking or running.
Click on the picture:
This graph shows my anaerobic threshold at the start of my base period as measured during a step test on a treadmill. Beginning from an initial speed of 5.6mph, I increase speed every minute and track the result. Initially, the relationship between the applied stress (i.e. increase in speed) and strain (heart rate) is linear. If I increase my speed 1 mph, my heart rate goes up by about 16 bpm.
However, when I get to my anaerobic threshold this relationship changes: as my speed increases from 8.5 mph to 9.5mph, my heart rate only goes up by 9 bpm rather than 16.
So why should I care?
The answer is that the anaerobic threshold is closely correlated to the effort that you can hold for an hour but, it isn't a linear relationship. If you go about 10% faster than your AT pace, this is about your 5k pace which you can probably only hold for 20-25 minutes. On the other hand, if you're 10% under, you can probably hold the effort for 5-6 hours: long enough to complete a half-Ironman!
For an even better explanation of thresholds, click here.
If you'd like to arrange a VO2max and Lactate Threshold test .... click here.