Garmin Training Effect Explained: What Those Two 0–5 Scores Actually Mean
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Garmin gives every recorded session two scores between 0.0 and 5.0: Aerobic Training Effect and Anaerobic Training Effect. They are separate numbers, calculated separately, and neither of them is a difficulty rating.
That last point is where nearly all the confusion comes from. Training Effect does not answer "how hard was that?". It answers "what did that session stimulate, and how much?" — a different question, and the reason a plodding long run can score higher on aerobic effect than the interval session that left you on your hands and knees.
The two scores, in one line each
- Aerobic Training Effect rates how much the session stimulated your aerobic system — the oxygen-using machinery behind everything from an easy jog to a half marathon. It is driven by intensity multiplied by time, so duration counts for a lot.
- Anaerobic Training Effect rates how much it stimulated your anaerobic system — the short, hard, above-threshold work you cannot sustain. It is driven by high-intensity efforts in distinct bouts, so duration counts for very little and intensity for almost everything.
Both come from the Firstbeat analytics engine Garmin uses throughout its training metrics, and both are scaled relative to your own current fitness as the watch estimates it. That has a consequence people rarely expect: as you get fitter, the same session scores lower. Nothing has gone wrong — the bar moved.
What the bands mean
Both scores use the same bands and labels on most Forerunner, Fenix, Epix, Venu and Vivoactive models:
| Score | Garmin's label | What it means in practice |
|---|---|---|
| 0.0–0.9 | No benefit | Too easy, too short, or — for anaerobic — nothing hard enough to register |
| 1.0–1.9 | Minor benefit | Some stimulus. What most easy runs should look like |
| 2.0–2.9 | Maintaining | Enough to hold your current level for that system |
| 3.0–3.9 | Improving | Enough to push that system forward, if you recover from it |
| 4.0–4.9 | Highly improving | A big stimulus. A key session, not a routine one |
| 5.0 | Overreaching | More than your fitness can absorb from one session |
The exact wording varies slightly between models and firmware versions — some devices say "Some Benefit" where others say "Minor Benefit" — but the bands themselves are consistent.
The "primary benefit" label
Most recent Garmin watches also print a short label describing what the session mainly did: you will see things like Recovery, Base, Tempo, Lactate Threshold, VO2 Max and Anaerobic Capacity.
That label is a summary of the same two scores, not an extra measurement. A session with a high aerobic score and a near-zero anaerobic score gets called "Base"; one with a strong anaerobic score gets called something nearer the top of that list. It is a useful shorthand for scanning your history, and the fastest way to notice that your "easy week" was mostly Tempo sessions. The available labels differ by device and activity type, so do not worry if yours shows fewer than someone else's.
Why your easy long run out-scores your intervals
Run 8 × 400 m flat out with long recoveries and your watch may hand you a high anaerobic score and a modest aerobic one. Run two steady hours at a pace you could hold all day, where nothing is hard, and you may get a high aerobic score and an anaerobic score of 0.0.
Both readings are correct. The long run accumulated two hours of aerobic stimulus, which is a large aerobic dose by any measure. The interval session accumulated almost none, because the aerobic system was barely engaged between reps — but it hammered the anaerobic one.
The scores are not disagreeing with your legs. They are answering a question your legs were not asked. Perceived difficulty tracks intensity; aerobic Training Effect tracks intensity and duration. Those two come apart constantly, and when they do the watch is usually right and your intuition is measuring something else.
If you want a number for how much a session will cost you, that is not Training Effect. That is training load and recovery time — which has its own set of problems.
5.0 is not a target
Garmin calls 5.0 "overreaching" and means it literally: the session delivered more stimulus than your fitness can productively absorb. One occasionally, in a race or a genuine peak session, is normal.
Chasing it is how people dig themselves into a hole. Fitness is built when a stimulus is followed by enough recovery to absorb it, and a week of 4.5s and 5.0s delivers plenty of stimulus and no recovery, so the adaptation never lands. The sensation is distinctive: you train hard, you feel permanently flat, and your numbers stall or slide backwards. If that is where you are, the warning signs of overtraining are worth reading honestly — and if you feel genuinely unwell rather than just tired, that is a question for a clinician, not a watch.
A well-built week is mostly "minor benefit" and "maintaining" sessions with a couple of "improving" ones. It looks unimpressive on the watch. That is the point.
Training effect and training load are not the same thing
These two get used interchangeably and they measure different things:
| Training Effect | Training Load | |
|---|---|---|
| Scale | 0.0–5.0, capped | An open-ended number, no ceiling |
| Question it answers | What did this session stimulate? | How much work have I accumulated? |
| Relative to you? | Yes — scaled to your current fitness | Partly: the number is absolute, the optimal range is personal |
| Adds up over time? | No. Each session stands alone | Yes. Sessions roll into your 7-day load |
| Best used for | Checking the mix of stimulus | Checking the volume of stress |
You need both. Two athletes can have identical 7-day loads where one built it from steady aerobic work and the other from repeated near-maximal efforts. The load numbers match; the weeks are nothing alike, and only Training Effect shows the difference.
That is what Garmin's load focus view is for: it buckets several weeks of training into low aerobic, high aerobic and anaerobic contributions and tells you which bucket is short. It sits inside training status, and it is the natural next screen after these two scores.
The one use I would actually trust
Do not judge single sessions by their Training Effect. Judge weeks.
Any one score can be thrown off by a bad heart rate trace, an unusual warm-up, heat, caffeine or an out-of-date fitness estimate. Across a week those wobbles matter much less, and the question the scores answer becomes genuinely useful:
- Is every anaerobic score 0.0? You have no top-end stimulus. Fine in a deliberate base phase, a problem if your race has a sprint finish.
- Are your "easy" days scoring 3.0+ aerobic? They are not easy. This is the most common pattern in self-coached training and the one that stalls progress — the zone 2 guide explains why.
- Is nothing in the week above 2.9? You are maintaining. Comfortable, but you will not improve from here.
- Is most of the week 4.0+? That is not a brave week, it is an unsustainable one.
Read as a weekly mix rather than a per-session grade, the two scores earn their place on the screen.
Why your anaerobic training effect is stuck at 0.0
This is the most common Training Effect complaint, and there are four real causes.
1. You genuinely did not do any qualifying work
Anaerobic effect needs distinct bouts clearly above your threshold. A hard continuous tempo run — uncomfortable the whole way, never truly flat out — can legitimately produce 0.0 anaerobic. So can a long hilly run where your heart rate crept up but never spiked. This is the explanation in most cases.
2. Your max heart rate is set too high
The direction here is counter-intuitive. If your stored maximum is higher than your real one, every effort reads as a lower percentage of max than it was, so genuinely hard intervals never cross into "high intensity" and your anaerobic effect flatlines.
Set it too low and the opposite happens: both scores inflate, easy runs get logged as threshold work, and the rest of your metrics go with them. Either direction corrupts Training Effect, which is why that one value is worth getting right before you take any of this seriously.
3. Your heart rate data never gets high enough to register
Wrist optical sensors lag at the start of a hard effort — sometimes for most of a short interval — and they tend to clip the peaks. On a session of 30-second repeats they can miss the entire point of the workout. A chest strap fixes this more reliably than anything else you can do.
4. Your device or activity type does not support it
Anaerobic Training Effect is not on every watch in the range, and on some models it is not calculated for every activity type. If you have never seen the number at all, check your device reports it before hunting for a cause.
When the scores are simply wrong
Occasionally you will finish an easy run and find a "highly improving" aerobic effect and a recovery time measured in days. Look at the heart rate trace before you believe it. Optical sensors fail in recognisable ways: a flat plateau at an implausible value (often locking onto your cadence rather than your pulse), a cold-weather start reading far too high, or a loose strap producing a sawtooth. Training Effect is calculated from that trace, so garbage in, garbage out.
Two honest limitations:
- You cannot make Garmin recalculate it. As far as I know there is no way to re-derive Training Effect for an activity already uploaded, even if you correct the data afterwards.
- The bad session keeps affecting you for about a week, because it also feeds your acute training load and recovery time. Deleting the activity removes that contribution — but it also removes a session you actually did, so it is a judgement call rather than a fix.
Going forward, a chest strap on quality sessions removes most of this class of problem.
The wider point
Training Effect is a good measurement wearing a misleading name. It tells you what a session stimulated — and then it stops, because it has no idea what you are training for, what you did last week, or what you should do tomorrow. The numbers are inputs, not instructions. A 3.5 aerobic effect is excellent news in a base block and a wasted Tuesday three days before a race, and no score from 0.0 to 5.0 can tell those apart.
The way past that is to stop grading sessions and anchor them to a boundary that means something physiologically: your lactate threshold, the intensity where lactate begins accumulating faster than you clear it. That line separates work you can sustain from work that is on a clock — and it can be measured rather than inferred, unlike your VO2 max estimate. If your watch will not give you a figure, that is a known and fixable problem.
Lactate Training, our app, syncs your Garmin activities and health data and builds a plan around threshold-based zones rather than a guessed maximum — the part the watch does not do. But the reframing is worth having either way: read the week, not the session.
If you want the rest of the watch's numbers decoded the same way, start with the full guide to Garmin's training metrics.
Frequently asked questions
What is a good training effect on Garmin?
There is no single good number — it depends on what the session was for. An easy run should score 1.0–2.0 aerobic and 0.0 anaerobic. A key threshold session might score 3.0–4.0 aerobic. A sharpening session might score above 3.0 anaerobic and very little aerobic. A good week is mostly low scores with one or two in the "improving" band.
Why is my anaerobic training effect always 0.0?
Usually because you did no qualifying high-intensity work — anaerobic effect needs distinct bouts clearly above threshold, and even a hard continuous tempo run can legitimately read 0.0. The other common causes are a max heart rate set too high, so hard efforts never register as high intensity, and wrist optical heart rate that lags and clips the peaks of short intervals.
Why does an easy long run have a higher training effect than my intervals?
Because aerobic Training Effect is intensity multiplied by duration, and a two-hour run accumulates a large aerobic dose even at low intensity. Your intervals scored lower on aerobic effect and much higher on anaerobic effect. Both are correct; they measure different systems.
Is training effect the same as training load?
No. Training Effect is a capped 0.0–5.0 score for one session, scaled to your current fitness, describing what the session stimulated. Training load is an open-ended number that accumulates across sessions and describes how much stress you have taken on.
Should I aim for a training effect of 5.0?
No. Garmin labels 5.0 "overreaching", meaning the session delivered more stimulus than your current fitness can absorb. One occasionally — a race, a genuine peak session — is normal. Repeatedly is how people end up training hard and getting slower.
Why did my training effect drop for the same session I did last year?
Because Training Effect is scaled to your current fitness. As your estimated fitness rises, an identical session is a smaller relative stimulus and scores lower. A falling score for a repeated session is usually evidence that you are fitter.
Scoring the session is easy; balancing the week is the work
Training Effect grades what you just did. Deciding what the next six days should look like is the part it leaves to you. Lactate Training syncs your Garmin activities and health data and builds a plan that distributes the hard and the easy for you, with zones set from your lactate threshold.