As a cyclist finishes their base training, it's important to evaluate how strong your aerobic base truly is. By using a metric called “aerobic decoupling” you can quickly and easily determine if your base work was effective and if you're ready to progress into harder high-intensity interval training. But before you can evaluate your aerobic fitness, you need to learn what aerobic decoupling is and how to use it effectively.
What is aerobic decoupling and why do we care about it?
If you're training with power, aerobic decoupling is a key measurement to evaluate as you perform base training. Aerobic decoupling is a numerical measurement of aerobic efficiency and endurance. It's representative of your body's ability to process oxygen and produce energy (as detailed in Biohacking Energy Systems) and is a marker of overall aerobic fitness.
Before you can appreciate the value of aerobic decoupling, here's a refresher about how your body produces aerobic energy and the concept of heart rate drift.
To produce energy, your body takes in oxygen through the lungs and passes it to working muscles via the blood stream. Oxygen and a fuel (fat, protein or sugars) are processed in the mitochondria to create Adenosine Triphosphate (ATP). ATP is the actual energy molecule that allows your muscles to contract and create pedaling force. Constant demands on the aerobic energy system can create a phenomenon known as heart rate drift.
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Heart rate drift occurs because your body is an organic system and it fatigues under use. For example, in a 40k time trial, you will be working as close to your functional threshold power as possible.
Initially, your body will recruit as few muscle fibers as possible in order to propel your bike forward. As your body continues to work at a constant level, more muscle fibers are needed to continue producing power. Your body recruits fresh fibers as some of the initially used muscle fibers begin to fatigue. The fatigued fibers can't produce as much force so your body calls on other fresh fibers to help. The more muscle fibers that are being utilized, the more oxygen is necessary to power them.
Your body requires more blood volume to transport oxygen as it recruits more muscle fibers. Increased cardiac output most commonly occurs via an increase in heart rate. This creates the phenomenon of HR drift. Combined with a constant power output, you have aerobic decoupling.
This increase in muscle fiber recruitment and increased oxygen demand creates aerobic decoupling. By definition, aerobic decoupling is a measure of how your heart rate reacts to a given steady power output. Typically, you'll find either an increase in HR for a given intensity or drop in power for a given HR.
*Note that aerobic decoupling is completely ruined by anaerobic efforts: measuring aerobic decoupling requires a completely aerobic effort.
What is aerobic decoupling used for?
Aerobic decoupling is a great measure of aerobic fitness. Essentially, the longer you can ride without experiencing significant decoupling, the more fit your are. It's also a measure of how fatigue resistant your body is.
As I've talked about in the past, fatigue resistance is one of the keys to building solid base fitness. You have to specifically train muscle fibers to be fatigue resistant during your training rides. Otherwise, you'll burn through your available muscle fibers and eventually end up cramping or bonking.
I use this measurement primarily in the base phase and early build phase of a training program. It's also a great way to determine if you'll be able to last for the duration of your “A” priority goals.
For how long should you be fatigue resistant?
Your level of fatigue resistance depends on the demands of your target events. If you're targeting a 50-mile road race, you'll need to be resistant for up to 3ish hours of aerobic work. Conversely, if you're training for criteriums, you'll need to be strong for around an hour. It's generally a good idea to be able to handle more stress than you really need to. For example, if you need to last an hour, it wouldn't be a bad idea to be resistant to fatigue over the course of several hours.
As a general rule, I want to see 5% or less aerobic decoupling for an aerobic workout lasting around the duration of your target event.
You can pull aerobic decoupling from plenty of sources. If you have a block of aerobic threshold work in one of your workouts, you can get a decoupling measure on that and get an idea of how your body handles fatigue. The more anaerobic interval work you've done before this aerobic block, the truer the measure of your aerobic fitness.
As you can see in the image, I've measured aerobic decoupling in a Golden Cheetah workout window. WKO and TrainingPeaks have tools to measure this as well. There are ways to measure it yourself, but the easiest way to do it is to use one of the major software suites. Find a 20 minute or longer SST or FTP type interval, select it and you'll be able to check your decoupling percentage.
Note that this measurement REQUIRES the use of a heart rate monitor and a power meter. If you're not training with both of those, aerobic decoupling is impossible to measure. Keep in mind that you don't need a power meter on your bike, either. You can perform this measurement using a power measuring trainer like an Elite Drivo, Wahoo Kickr, Cyclops Hammer or Kurt Kinetic Smart trainer.
Aerobic decoupling, while a valuable tool, is far from infallible. You'll need to be sure your aerobic sessions are performed to specific parameters which you can replicate over and over again. There are also a number of situations which can adversely affect your aerobic decoupling measurements.
Dehydration is one of the principle conditions that can have a profound impact on your aerobic endurance. Even as little as 3% loss in body water weight can significantly impact your performance. Heat and hot conditions, especially when poorly acclimated, can also wreck your performance metrics. Both of these are important to control for in your aerobic testing. If either of these conditions (and many others) are present, your aerobic decoupling numbers will be misleading and often completely false.
What workouts can help reduce aerobic decoupling?
If you're seeing significant aerobic decoupling on your aerobic intervals, first make sure you're not dealing with any of the conditions above. If you truly do have deficits in your aerobic conditioning, look to workouts like muscular endurance and sweetspot training. Muscular endurance is a great tool to help build fatigue resistance at all output levels, not just aerobic levels. Sweetspot training intervals are highly repeatable and easily worked into almost any workout.If you're training for a longer goal event such as a 4 or
If you're training for a longer goal event such as a 4 or 5-hour gran fondo or a long road race, don't try to do 4-hour intervals. Commit to several back to back to back days of 1.5 or 2-hour intervals to help accumulate fatigue over the course of several days. The multiple days of work back to back will create accumulated fatigue that will be similar to doing several long intervals in one day.
Ask for a little help!
If you've got a question about how aerobically fit you are, head on over and ask me! Don't forget that if you're struggling to meet your training goals, you can pick from a ton of great training options in my downloadable training plan store, including my Unbreakable Core Stability module, Full Season Training Solution, and Advanced Full Season Training Solution. You can also get a ton of great training tips FOR FREE by signing up for the Tailwind Coaching Newsletter. You'll also get a free bonus training plan, updates, and exclusive discounts like the Unbreakable Core Stability discount!
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