This test has been referenced multiple times over the past year or
so. As many members ask about it I am copying the Original Post
(by Koffee Brown) here.

PLEASE DO NOT RESPOND TO THIS POST.

THE TEST:

Here's the test for anaerobic threshold. You can get it from Sally Edwards/Sally Reed book- "The Heart Rate Monitor Book for Outdoor and Indoor Cyclists", pp. 92- 94. The test is done on a stationary bike or indoor cycling bike.

The top of Zone 3 is 80%. The top of Zone 2 is 70%. The bottom of Zone 2 is 60%. The bottom of Zone 1 is 50%.
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2X20 Anaerobic Threshold Test

This is an anaerobic heart rate test designed by David Martin, Ph.D. at Georgia State University. The goal of this workout is to sustain the highest heart rate number you can for 20 minutes, followed by a 5 minute recovery and then sustain the same number again for 20 minutes. After completing both 20 minute intervals, answer the question: Was that hte hardest I could work for the duration of time (40 minutes)? If the answer is yues, then that heart rate number is an excellent estimate of your anaerobic threshold heart rate.

Purpose
Anaerobic theshold is one of the ways of measuring fitness. The higher the percentage of maximum heart rate you can sustain for the duration of the test, the fitter you are. This translates into being able to cycle faster for a longer duration. If you have never done this test before you may want to be conservative the first time until you get the feel for what is happeniing and what is expected. Retest in a month or six weeks to see if you are getting fitter. It is important that you are fully rested before doing this test and that you give yourself a minimum of 48 hours of rest from riding above heart Zone 3.

Workout Plan
Warm up for 5 minutes to the bottom of Zone 2, then gradually increase heart rate for the next 5 minutes until you reach the heart rate number that you thinnk you can sustain for 20 minutes. Sustain that number for 20 minutes. You may choose to use cadence, resistance/gearing or any combination you wish to sustain the heart rate. After 20 minutes, recover to the bottom of Zone 2 for 5 minutes. Make sure you drink plenty of water and allow your legs and body to relax.

After 5 minutes of recovery begin to increase your heart rate agian over the next 3 minutes until you have reached the same heart rate number that you sustained for the first 20 minutes. Sustain that heart rate for a second 20 minutes, then warm down over the next 7 minutes to Zone 1.

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Keep in mind, you are looking for ONE NUMBER.... not a RANGE OF NUMBERS... Often, I'll run through the first 20 minutes with my students, then when I talk to them in the 5 minute break, they say something like, "oh, I was between 156- 160". Aaaaaaaugh!!!!!!!!!! You are looking for that one number, not a range. So if it's 160, it's ONLY 160... not a range of different numbers that's "around" 160.

This is just a taste of the test, but there's a performance based heart rate chart that you can look at to find that number for anaerobic threshold (80%), and easily read the chart for the rest of the numbers in your heart rate ranges. That's why I suggest you get the book. It's also a great book because it gives outdoor and indoor training exercises you can do to improve your fitness level. If you don't have the book and you want to do the test right away, go to the website: http://www.heartzone.com/index.shtml
Over there, click on the link that says "HEART RATE CALCULATOR". About halfway down the page, there is a heart rate calculator that you can use that will break your heart rates down into zones. You will have to fiddle around with max heart rate, since you didn't test for max hr, but if you keep entering numbers in the max heart rate, you'll eventually find the correct numbers to use. I used my example of 160 as my anaerobic threshold (80%), and I started by entering 195 as my max (guessing). It was a bit low, so I entered 200 as my max hr, and this time, I got correct numbers, because the 80% on the chart came out at 160. I hope that makes sense. If it doesn't, get the book.