Threshold – What is it?
The term “threshold” is used in many ways in terms of sports and endurance, such as anaerobic threshold (AT), lactate threshold (LT), maximal lactate steady state (MLSS), onset of blood lactate (OBLA). Exercise physiologists have known for a long time that as you increase the intensity of exercise you reach a point where lactate begins to accumulate in a person’s blood, and this their LT. It is an indicator of the athlete’s endurance ability. Lactate is a good thing since it is a fuel for the body during exercise, but when you create more than you can use, it builds up in your muscles and will limit what you can do.
For cyclists who use a Power Meter, this same threshold concept is called FTP, or Functional Threshold Power. Just as you might see what heart rate you can hold for 1 hour to determine your LT, FTP can be determined by seeing what power you can average for a one hour time trial. Knowing your FTP can allow you to set power zones for training, similar to heart rate zones.
In the book “Training and Racing with a Power Meter” by Hunter Allen, and Andy Coggan, a test protocol is provided to determine your FTP. Not many want to do a one hour time trail periodically just to get this number so their test involves a series of steps, leading up to a 20 minute section where you try to go close to your threshold. From this test, you can determine your FTP. The first time I did this test last year, I wrote it out on a piece of paper and taped it to my handlebars, trying to read the next step while I was in the middle of an intense setp. The Workout Feature of the Garmin Edge products makes this so much better.
Garmin Connect Workout
The first step is to log into Garmin Connect and set up a new workout. Using the test protocol, I added 11 steps. This way I can use the Garmin Edge 800/810 to guide me through each step. Note for each step I selected the time and what to measure. During the warmup I wanted to keep my heart rate in the range of 110 to 115 bpm, so that was the first step. The test protocol includes some one minute segments at high cadence, so I selected cadence between 95 and 105 for one minute for those steps, and so forth. For some steps I could either set a target for Power or Heart Rate but I decided to use Heart Rate since I am more familiar with my threshold for that.
Getting Ready for the Test
Once you have the workout setup in Garmin Connect, you connect your Garmin Edge 810 to your computer and send the workout to it.
Next pick the route to do the workout on. Ideally it will be one where you can ride without stopping. For me, I prefer to do the two segments where I need to get my heart rate up high to be on a hill climb. The only negative is that I need to do a recovery 10 minutes while climbing, but that worked out okay for me. I decided to do the test riding from home, and then climbing Squaw Peak in Utah. This allowed me to do the warmup steps on the way the the climb. You could decide to do all of the steps on a bike trainer, but that would not be very interesting to me.
Now you are ready to run the test protocol, letting the Garmin guide you through each step. The workout screen includes a count down time, and the parameters you are trying to achieve, in this case I was on step 10, trying to hold my heart rate just below threshold for 20 minutes. If I am in the desired zone, a message will show at the bottom, then disappear. If I am outside the desired range for that step I will get a similar message.
These messages at the bottom auto clear. The main screen shows your current step at the top, the prior step and your next step below. When I reach the end of one step, a message at the bottom appears briefly with details of the new step, telling me to speed up or slow down to get into the desired range.
A simple approach when you finished is to see the average power you generated during the 20 minute test. Your FTP will be about 5% below that since the FTP is for a full hour. Since I ended up with 206 watts for 20 minutes, that means a FTP at my current condition of 206 – (206 x .05) = 196 watts. Remember that watts is not as important as watts per kg, and since I am a lightweight small guy, 196 watts is much better than it would be for a large cyclists, who needs to put out more watts to go as fast, especially on a hill climb.
If you are a STRAVA user, you can get these type of plots. Here the current ride, or this test is plotted against my best power vs. time over the last six weeks. The test was successful because the average power for 20 minutes was just as high as my best for the last 6 weeks. The test protocol is not to see how much power you can put out for 5 minutes or 5 seconds, but to determine your FTP, or threshold by using a 20 minute segment.
Another good program (free) is Golden Cheetah. Load the ride into this program and you get all types of analytical tools. From the plot below you can see that my 20 minute critical power is below what I did last year. It is a clear indication that I am not in the same condition as my best condition last year where you FTP was at least 20 watts higher.
Hunter recommends that you run this test protocol a few times a year to determine your current condition. Using the workout feature in Garmin Connect and the Garmin Edge 810, you can easily do this and the test is set so it is not as exhausting as trying to do a one hour time trail. Just using a heart rate alone makes it difficult to determine fitness since your heart rate is not a direct measurement of your power output, being affected by things such as fatigue and other physiological aspects. That is what the Power Meter is becoming so popular with cyclists.