What is DFA a1 and how could it be useful as a training tool?
You may have seen the term DFA a1 popping up on forums or blog posts relating to effective base training, or its use as an alternative to getting tested at a sports laboratory. This article defines what it actually is, how it works, and the potential benefits of using it to optimise your training.
In my last article, Using Training Zones I discussed training zones - how they were useful, but also their limitations. One such limitation was the assumption that we all perform exactly the same, day in and day out, as we did on our ‘reference’ test day, which sets our training zones. Another is that we are all identical and that operating at 80% of my threshold will have exactly the same impact for both you and me (possibly so, but training status, muscle fibre type distribution, and energy substrate utilisation for example could all have an impact on this). That’s not to say that training zones are useless - once accurately set, they are a great guide and, in most cases, will get us to the right place to create the training adaptations we are looking for.
However, what if you are one of these outliers? Or if you are often coping with very different levels of fatigue or just have a key training session to do and want to make sure that you are really making the most of it? This is where DFA a1 offers an advantage, and to explain why I’ll need to define what it is.
DFA a1, or ‘detrended fluctuation analysis alpha 1’, is a mathematical function of your beat-to-beat heart rate variability. As such, it’s essentially the same as HRV (heart rate variability) but with an additional mathematical model applied to the measurements so that patterns in heart rate variability can be detected. These patterns, which change based on how the body is responding to exercise, have been discovered to be a good predictor of your aerobic threshold. Just to ensure we are all on the same page, I’m not referring to the anaerobic threshold here (FTP, lactate threshold, etc.). To explain, I’ve pulled this from my ‘best cycling metrics blog’:
“There are actually 2 thresholds generally defined during testing. The one you are probably most familiar with is your FTP or Anaerobic Threshold. The aerobic threshold happens earlier on (so at a lower power or heart rate) and represents the highest power or pace you can sustain without increasing your lactate levels from baseline. Why is this important? Well, it represents your maximum ‘cruising’ speed, where you are burning the most amount of fat as a fuel (you are likely also using some carbohydrates, but not much). This is important as it represents your ‘long duration’ max power, not your 45 – 60 min max power. If you are well trained enough, you could likely keep this intensity up for many hours, as we all have very large fat reserves when compared to carbohydrates, and due to the low usage our carbohydrate stores should be able to be kept topped up. This intensity is the cornerstone of base training and aerobic adaptations.”
So DFA a1 can be used to define the aerobic threshold in a similar way you might test for your anaerobic or lactate threshold - with a step ramp test (I’ll explain what you need and how to do this in the last of the 3 articles). Previously, the only way to determine this would be to visit a sports testing lab.
As mentioned above in the Training Peaks article linked above, Zone 2 training is critical for any endurance athlete and should be the zone you spend the most time in. However, an assumption is being made here, which is that your aerobic threshold lies in zone 2. This is a little bit like relying on the 220-age formula for working out maximum heart rate - it could be bang on, but for a few people, it could be a long way from the mark. Testing TTH athletes have shown us that an aerobic threshold could be anywhere from the bottom to the middle of zone 1, up to way into mid-zone 3. This is where the DFAa1 determines aerobic threshold testing is really useful, and you can find it out for yourself using the equipment a lot of us already have - either a sports watch capable of recording HRV data or a phone app, plus a home trainer. Working at this threshold not only means you are utilising the maximum amount of fat and therefore working your mitochondria as hard as possible but also maximising lactate clearance/utilisation.
Another benefit is that as well as working your endurance system as hard as it will go, you are doing so without creating any more fatigue than necessary. This means that you could potentially either increase the amount of aerobic training you can do (bigger volumes), or save more energy via less fatigue build-up for those higher-intensity sessions another day. Either way, it’s optimising your endurance training session.
It’s also a great predictor of longer course endurance performance, so can be tracked as a metric to give race predictions and also to show the progress (or otherwise) of your current training program.
So far I’ve been discussing the use of this metric as an output of a test - however where I find it most useful when used in conjunction with either one of a few phone apps (Fatmaxxer, HRV Logger), or a Garmin app called Alpha HRV. These apps allow you to see where your aerobic threshold is in real time, which can be really helpful when you are carrying a little more fatigue than usual. As mentioned in my last article, no one can assume they can put out exactly the same performance day in, and day out. There will be good days and bad days. So the snapshot measurement taken on the day of testing is a great start but may not always be 100% accurate.
You can either judge where your current performance might be on feel and adjust or use some kind of physiological measurement to help guide you, such as HRV. HRV indicates which side of your autonomic nervous system is dominating. If the parasympathetic or fight or flight system is stronger, then you are more fatigued and should possibly back off, and if the sympathetic system is higher, then you are coping well with your training load and maybe could step things up a bit.
If you recall, DFAa1 is derived from HRV measurements, so the live values you can view from the apps show you, in real time, how your body is responding to the effort you are producing. If you find you get up to your aerobic threshold earlier than you were expecting (at a lower power/output), then this is possibly not a good day for you. If the inverse is the case then you may want to push things on a bit. Whatever kind of day you are having, you can still ensure that you are operating at your true aerobic threshold and therefore getting the absolute maximum benefit possible from your endurance workouts.
The use of DFA a1 to determine your aerobic threshold is in its early stages, and while there have been a number of studies done that show good results with regard to group averages, individual results can vary. This is due, in my opinion, to the fact that it seems fairly sensitive to the method, equipment, and use application. As such, I believe it's critical to take a well-considered, researched approach when using it, and I’ll be explaining what you’ll need and how to do this in my last article.
Kevin opened a B&B for cyclists in France in 2014, & then a year later decided to start a cycle coaching (level 3) qualification. This was mainly in order to be able to better support his guests (but also to make his own training more effective too). At the B&B he runs the odd training camp for cyclists but mainly offers coaching advice while guiding guests. An engineer by background, he happy diving into all sorts of training data, but also understanding that coaching is about much more than just the numbers!
After being introduced to triathlon by a good friend & then taking part in races for a couple of years he decided that a level 2 coaching course with British Triathlon was the way forward, completing this in 2019.
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