What Is Garmin Training Effect: Everything You Need to Know

Your Garmin running watch can provide you with a lot of advanced data. One of these data points is Garmin training effect.

What is it? How it is calculated? What does it mean?

Keep on reading to find out.

What Is Garmin Training Effect?

Every time you complete an activity, Garmin assigns it a training effect score. This is an estimate of how much impact that activity would have on your fitness.

The longer and harder your activity, the higher the score. This score is mapped onto a five point scale to give you a general idea of the activity’s effect.

The five point scale is:

  • 0 – No Effect
  • 1 – Minor Effect
  • 2 – Maintaining Fitness
  • 3 – Improving Fitness
  • 4 – Highly Improving Fitness
  • 5 – Overreaching

Notice that the highest score – 5 – is called “overreaching.” This is because too much training effect isn’t a good thing. You need a balance of hard training and recovery to improve.

In a balanced training plan, the majority of your days should be 2’s and 3’s while your hard workouts might be 4’s and the occasional 5.

Difference Between Aerobic and Anaerobic Training Effect

This number is also broken down into two categories: aerobic training effect and anaerobic training effect.

The aerobic training effect is more focused on sustained activities and endurance.

For distance athletes, your fitness is mostly determined by your bodies ability to use oxygen to create energy. Any kind of long, sustained exercise will improve this – whether it’s an easy run, a tempo run, or a progressive long run.

The longer and harder the effort, the higher the training effect.

The anaerobic training effect, however, is focused only on your time spent running fast.

Running at high speeds – think racing a mile or an 800m – requires your body to create more energy than it can through aerobic pathways. But it can only do this for short bursts.

The anaerobic training effect is determined by the periods of your activity when you are running faster than your estimated VO2 max. The more, longer, and faster these intervals, the higher the training effect. The fewer or slower these intervals, and the lower the training effect will be.

How Is the Training Effect Calculated?

The calculation for training effect is based on EPOC – excess post-exercise oxygen consumption.

This is the amount of oxygen your body keeps using after you’re done exercising while trying to get back to a state of normalcy. It’s also a good proxy for measuring how hard a workout is. A higher EPOC means a harder workout.

Based on your heart rate during an activity, the pace of the activity, and the duration of an activity, Garmin can estimate what that EPOC is.

Once that is done, Garmin uses an algorithm to map that value on to the five point scale. This five point scale takes into account your training history and fitness level.

This is individualized because two individuals completing the same duration of workout at the same intensity would have the same EPOC on paper – but not necessarily the same training effect. A 20 minute tempo run for an out of shape newbie is much more demanding than a 20 minute tempo run for a veteran runner.

For the anaerobic training effect, a similar process is used. However, the algorithm only looks at the EPOC generated when you are running faster than your VO2 max. It also takes into account how many intervals you ran, their duration, and the pace relative to your VO2 max.

Examples of Training Effect

What does this look like in practice?

Here are a few examples of runs and workouts that I’ve done, and how Garmin’s training effect “scored” them.

As one example, let’s consider a typical “easy” run. In this example, I ran 6 miles with an average pace of 8:56 / mi. That’s pretty solidly in my easy zone. My average heart rate was 139. Again, in the easy zone, although by the end of the run it was starting to creep up closer to 150.

This was an aerobic training effect of 3.5 and an anaerobic training effect of 0. There were no intervals spurts of faster running in here.

Meanwhile, a recent long run (14 miles @ 10:12/mi pace, avg heart rate of 136) netted a training effect of 3.9. But a harder progression run (12 miles, 6 easy and 6 @ 7:25/mi) netted a training effect of 5.0. The progression run was clearly harder than the easy long run.

And here’s an example of a harder workout. This was 12x400m at around mile pace. It was a very hard workout.

In this case, you can see the anaerobic training effect is not zero. It scored 3.4. Meanwhile, the activity still had a 4.1 aerobic training effect – likely thanks to the extended duration of the session and the addition of some cool down mileage at the end.

What Could Make Your Training Effect Inaccurate?

As with all of Garmin’s metrics, this isn’t foolproof. And there are some things that can go wrong with the algorithm.

For example, if your heart rate data during the activity spikes due to cadence lock, you’re going to get inaccurate data. This happens to me on occasion, and if the training effect is higher than expected it’s usually an indication to me that something went wrong with my heart rate sensor. This is a good reason to make sure that you’re using a heart rate strap, like the HRM-Dual, if you’re going to be relying on this data in a meaningful way.

A similar problem involves the max heart rate and heart rate zones set on the watch. Garmin uses these heart rate zones to estimate how intense your activity is. If the max heart rate is too high, it’s going to underestimate the training effect. If the max heart rate is set too low, it will instead overestimate the training effect. This is why you want to make sure that you a) use a heart rate strap and b) perform a real max heart rate test.

In part, this algorithm is also tied into your VO2 max. Since VO2 max isn’t a perfect estimate on its own, any issues with your VO2 max estimate will also render your training effect inaccurate.

Finally, anything that messes with your heart rate – heat, humidity, fatigue, illness – is also going to make it hard for your Garmin to determine exactly how hard a run is. If your heart rate is higher than usual, the algorithm is going to assume you worked really hard. But it’s possible that there was a confounding factor in there.

So How Should You Make Use of Training Effect?

At the end of the day, Garmin training effect is a useful data point – but it’s hardly perfect and you should take it with a grain of salt.

Personally, I think my Garmin tends to slightly underestimate my VO2 max and overestimate my training effect. So in my mind, some of the 5’s I see are probably really 4’s, and some of the 3’s are really high 2’s.

What I do look for, though, is that there’s a significant difference between my easy runs and my workouts. A typical morning run will usually be a training effect of 2-3, and that’s what I expect. Meanwhile, a harder workout is probably going to be a 4-5.

If I noticed something was off, then I’d probably look for some other data points to confirm whether or not my training is working effectively. For example, if something intended to be a hard workout only rated a training effect of 3.0, I might reconsider the target pace. If the original pace was too easy, that’s a sign I might want to speed up a little bit in the next workout and keep pushing things.

How do you make use of Garmin training effect? Do you find it useful? Leave a comment below and let me know.

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