Anaerobic Threshold Field Test
Knowing your anaerobic threshold can be critical when you first begin to get serious about your training. But it doesn’t matter if you’re a “racer” or not because anaerobic threshold (AT) represents our fastest steady-state effort. It’s the effort that a cyclist can maintain for roughly 45 minutes to an hour, and any cyclist interested in riding a little easier or more efficiently can benefit from learning their AT. Of course, we won’t spend every moment of a 70-mile ride or race at AT, but we will have work up to and above it quite often, especially as the terrain steepens.
We call it the functional “fastest steady-state effort” because of what happens just above AT. Just a few percentage points above this effort and our ability to generate power for very long decreases rapidly.
For instance, this is a common scenario. A cyclist may be able to ride for 3 hours at 180 watts, and they can spend 45 minutes at 235 watts — which would make that roughly their anaerobic threshold. But if that athlete works up to 260 watts, now they can only hold that effort for 6-7 minutes. An 11% increase in power causes an 86% decrease in exercise duration. If this athlete were doing a 70.3 triathlon (which has a 56-mile bike section) they could severely impact their bike split by going above their AT by just 10% for just a few minutes, since it could cause them to slow down drastically to recover from their above-threshold effort.
Isn’t a physiology lab the best place to get tested?
You can certainly find a human performance lab and get your AT tested a number of different ways, from actual graded lactate blood draws, or a VO2 test. But expect to pay $75-$300 for this service each time, which really adds up when you figure that you’ll want to retest regularly to gauge progress and update your training zone intensities.
Many times the lab tests are difficult to get good numbers out of as well for a couple reasons:
- The lab procedure can be very foreign to the rider — many athletes aren’t used to breathing through the mask needed for the VO2 test, or the fit and feel of the ergometer/stationary bike can be vastly different from their own and so they don’t perform up to their potential.
- There’s also a certain amount of anxiety to perform well — I see many athletes start out too hard or have the test advance too quickly so that they’ve blown up within 6 or 7 minutes when ideally we’d like them to go 10-13 minutes.
What if I’m only using perceived exertion?
If you’re not training with any data like heart rate or power, and solely going off perceived exertion, you won’t need a test for the traditional reasons like setting training zones, but it can still be helpful to gauging progress. Your focus will be a little different and it’ll be important to use the same course to ride on each time.
If you can find some open road that allows you to ride for roughly 20 minutes uninterrupted and is affected less by the wind (that’s why I like to use climbs), you can set a baseline time on this course and repeatedly go back to it for a time trial re-test to see how much quicker you cover the same distance.
Knowing that when you began your training the course took you 19:45 and now you can do it in 19:28 is helpful, but I also find that time trial tests give us insight into how hard we can push in race situations. We get a better idea of where our limits are and gets us more comfortable pushing into them.
Having an easy to replicate field test will save you time and expense. Plus it’s not terribly difficult to do.
So here’s how you do it:
- Begin by pedaling easy to warm up — I recommend usually 15-30 minutes.
- After your warm-up, do a 1-minute effort above your threshold — I don’t care how much above, just make sure that you can finish the 1-minute interval as strong as you started it.
- Pedal easy for 3-4 minutes.
- Do one more 1-minute above-threshold interval at the same intensity as before.
- Pedal easy for 5 minutes.
- Now ride 20 minutes at as hard a steady-state effort as you can, while you either record your heart rate or power (or both).
- If your computer/device isn’t capable of recording then do the test on an indoor trainer and have an assistant help you record these numbers around every 30 seconds
- Recover and pedal easy for the remainder of the ride — often I will schedule this at the beginning of a long weekend ride so that the cyclist can kill two birds with one stone, by getting in a test and a long ride on the same day
Now we can take the data from the 20-minute effort and we want the average heart rate and/or power from it. Take that average and multiply by 0.95.
[20-minute HR/power average] X 0.95
This will give you a more than reasonable estimate of your anaerobic threshold.
Is it perfect? No, but it is very close and more than accurate enough to plan a training program around. I’ve run this test side by side with athletes that have undergone a full VO2 lab test and the difference is usually just a couple watts.
How to make the AT field test as accurate as possible
- You want to make the effort as steady as you can. Starting too hard and then fading or going too easy and having to pick up the effort toward the end will introduce more variance into your data. Gauging your effort appropriately is difficult to do, and learning this skill is key for every endurance sport. This is another side benefit of testing regularly, since it allows you more practice at pushing and holding an effort for 20 minutes.
- Test the same way every time — either the same course or the same calibrated setting indoors.
- Know that your power will be different on the flats versus climbing — so if you plan to race on more flat terrain you should test on the flats or subtract 10-15 watts from your climbing power average to estimate your AT power on the flats.
- You don’t need to be fully tapered, but don’t test right after a difficult build phase finishes — give yourself at least a day or two (or three) of easy to moderate rides. Many cyclists find it’s difficult to test immediately after a day off the bike completely as well, so try to get in a moderate ride the day before. If a day off can’t be avoided then give yourself a longer warm-up.
There are other protocols out there for testing anaerobic threshold, but I find this method to be the one that produces the best results and is the easiest to implement. Others use shorter work intervals than the 20 minutes here, but I think when the work interval is much shorter then the mathematical factor employed creates more of a chance for error. Additionally 20 minutes at just above threshold is still pretty easy to recover from, so it doesn’t impact a training plan too heavily.
Want more information on how to track your effort with power, heart rate, or perceived exertion? Check out my article on the strengths of each method of gauging effort.
Now you need to put this information into action and train with it. Take a look at my article on how to safely get started implementing intervals on the bike.
So get testing and up your game this year!
He lives with his wife and two kids and runs multiple businesses in Grand Junction, Colorado.