Runna vs Garmin Coach: A Side-by-Side Test

Both apps will hand you a 16-week marathon plan in under three minutes. The plans will not look alike, and the reason they don’t look alike is not branding. It’s that one of them builds your paces from the race time you typed in, and the other builds them from what your watch has measured you doing.

That difference decides almost everything downstream: how fast your easy runs are, how much of your week is spent hard, whether your volume ramp is defensible, and what happens the week you catch a cold. So I generated both plans for the same runner on the same day and audited the output.

The test setup

The profile I used is deliberately ordinary, because most of the people asking this question are ordinary:

• 38 years old, four runs per week, 8 weeks averaging 40 km/week
• 10K in 47:30 six weeks ago (4:45/km)
• Garmin Forerunner 265: VO2 max estimate 47, lactate threshold pace 4:38/km, resting HR 52
• Goal marathon 3:45:00 (5:19/km), 16 weeks out
• Long run on Sunday, Strava connected, no injury history

Runna: marathon plan, 16 weeks, 4 runs/week, goal time 3:45, strength add-ons off so the running load was comparable. Garmin Coach: adaptive marathon plan in Garmin Connect, same race date, four running days.

One caveat before the numbers. Both products ship changes constantly, and Garmin Coach’s marathon plans in particular reshuffle themselves as your data accumulates, so treat the specific sessions below as one snapshot of a configuration rather than a fixed spec. The method of auditing them is the part that keeps working. If you’re triangulating across more than these two apps, the broader comparison of how each one builds progression sits on the pillar page at /ai-coach-apps/.

Where the paces come from

This is the single biggest divergence, and it shows up in the first week.

Notice what’s inconsistent there. Runna’s threshold pace (4:52) is slower than the watch’s measured lactate threshold (4:38), because Runna anchored to a 3:45 goal rather than to the 47:30 10K. Garmin’s threshold is bang on the measured figure. Meanwhile Garmin’s easy range is 25 seconds per km slower at the top end, which over a 29 km long run is roughly 12 extra minutes on feet at a lower cardiac cost.

Then I ran the tell. Same profile, same everything, goal changed from 3:45 to 3:30:

RUNNA, goal 3:45 → 3:30
  easy       6:00–6:30  →  5:45–6:15   (-15s/km)
  marathon       5:19    →  4:58       (-21s/km)
  threshold      4:52    →  4:34       (-18s/km)
  5K reps        4:28    →  4:14       (-14s/km)

GARMIN COACH, goal 3:45 → 3:30
  easy       6:15–6:55  →  6:15–6:55   (no change)
  threshold      4:40    →  4:40       (no change)
  VO2 reps       4:20    →  4:20       (no change)

No new physiological data went in. A typed number moved, and Runna’s entire prescription moved with it. Garmin’s didn’t budge, because it never used the goal to set pace at all; it uses the goal to decide whether the plan shape is plausible and to set race-pace work later.

Neither behaviour is wrong. Runna is running goal-backwards periodisation, which is how a lot of good human coaches work, and it’s genuinely motivating to see the paces that add up to your target. But it means the app cannot tell the difference between an ambitious goal and a fantasy one. If you type 3:15 off a 47:30 10K, you will get a 3:15 plan and you will get hurt trying to run it.

Volume progression, week by week

Weekly running kilometres as prescribed:

Week-on-week jumps look alarming in both (Runna goes 46 → 62 into week 9, a 35% rise), but that’s an artefact of down weeks and it’s not the right metric. Use the 4-week rolling block average instead, which is closer to what your tendons actually experience:

4-week block averages (km/week)
             wk1-4   wk5-8   wk9-12   wk13-16
Runna         44.5    53.5     62.0      52.5
  block-on-block           +20%    +16%
Garmin        39.3    45.5     50.5      44.0
  block-on-block           +16%    +11%

Runna takes a 40 km/week runner to a 68 km peak: a 70% increase in eleven weeks. Garmin takes the same runner to 56 km, a 40% increase. Both are inside the range a coach might write, but only one of them assumes your 8-week 40 km base was comfortable rather than maximal. Runna never asked which it was.

The long run, and one jump worth deleting

Runna’s Sunday progression ran 16, 18, 21, 16, 23, 25, 28, 19, 29, 32, 26, 22, 32, 26, 18. Garmin’s was flatter and capped lower, topping out at 28 km and switching to time caps (around 2h30) once the estimated duration got long.

The line that needs attention is Runna’s week 8 to week 9: 19 km to 29 km. Ten kilometres added to your longest run of the fortnight, +53%, immediately after a recovery week. On a 4:45/km 10K runner that’s roughly 60 extra minutes on feet compared to seven days earlier. I’d cut it to 25 km and accept losing nothing, because the long run either side of it does the aerobic work anyway.

Worth being fair about the other number, though. Runna’s week 10 has the long run at 32 of 66 km, 48% of weekly volume. Garmin’s week 13 is 28 of 58, also 48%. That’s not an app flaw in either case. It’s what happens when you choose four running days for a marathon, and the fix is a fifth easy day of 8 km, not a different subscription.

How each one behaves when the week falls apart

I simulated two scenarios.

Travel week, two runs instead of four. Runna leaves the missed sessions in place, greyed out, and carries on with the following week exactly as originally written. You can tap into the week and shift or swap sessions manually, and you can ask it to regenerate, but the default is that the plan holds its shape and you absorb the gap. Garmin Coach rewrites the next week without being asked: after two missed days it pulled the following Tuesday’s threshold set back to a shorter version and trimmed about 6 km off the week.

Five days off with a chest infection, Body Battery in the 30s and HRV Status flagged unbalanced. Garmin’s response was visible within a day: the suggested session on return was 35 minutes easy, and the plan’s next hard day slid by 48 hours. Runna’s plan was unchanged, because nothing in the illness reached it. Runna reads workouts, not readiness. If you skip five sessions it knows; if you complete five sessions while sick, it sees five completed sessions.

That asymmetry is the practical case for Garmin if you’re the sort of runner who does what the app says. It’s the practical case against Garmin if you’re the sort who finds the auto-adjustments demoralising, because a run of low readiness scores will quietly sand the intensity out of a training block and you’ll arrive at the start line undercooked and unsure why.

Intensity distribution

Taking week 9 from each plan and converting to time rather than distance:

RUNNA wk 9 (66 km, ~385 min)
  Tue  3 wu + 8x800 @4:28 (2' jog) + 2 cd     6.4 km @ VO2   28.6 min
  Wed  10 km easy
  Fri  2 wu + 3x3 km @4:52 (3' jog) + 2 cd    9.0 km @ LT    43.8 min
  Sun  29 km, final 8 km @5:19                8.0 km @ MP    42.5 min
  → 114.9 min at or above marathon pace = 30% of weekly time
  → 72.4 min at or above threshold      = 19%

GARMIN COACH wk 9 (52 km, ~320 min)
  Tue  4x6' @4:40, 2' recoveries                             24.0 min
  Thu  10 km easy
  Sat  12 km incl. 20' @5:25                                 20.0 min
  Sun  26 km easy
  → 44 min at or above marathon pace = 14% of weekly time
  → 24 min at or above threshold     = 7.5%

If you hold to something like an 80/20 split, Runna’s 30% is over and Garmin’s 14% is under. For a 38-year-old on four runs a week, three of which contain quality, Runna’s week is the one I’d expect to produce a niggle by week 11. For a runner chasing a specific 3:45 with a hard ceiling on training days, Garmin’s week is the one I’d expect to leave race pace feeling unfamiliar.

Cost, hardware, and what you actually give up

Runna is roughly £15.99 a month or about £100 annually, so a 16-week block costs around £60 to £64 paid monthly. For that you get the full plan visible end to end from day one, physio-built strength and mobility sessions, pace targets pushed to Garmin, Apple Watch, Coros and Suunto as structured workouts, and Strava integration (Strava acquired Runna in 2025, and the integration reflects it).

Garmin Coach costs nothing beyond the watch, but the adaptive marathon and half plans need a reasonably current device, so check Garmin’s compatibility list before you plan around it. What you give up is visibility: you see the coming week in detail and not much beyond it, which makes it genuinely hard to book a tune-up race or plan around a wedding. You also give up strength programming entirely, and you give up the ability to override without fighting the algorithm.

Audit either plan in fifteen minutes

Export your last 12 weeks from Strava (Settings → My Account → Download or Delete Your Account → request archive) and run three checks on whatever plan you’re handed:

1. PACE SANITY
   Is prescribed threshold pace within ~10s/km of your
   watch's lactate threshold pace, or of (recent 10K pace + 8s)?
   Runna in this test: 4:52 vs measured 4:38 → 14s SLOW, goal too soft
   If it's 15s+ FAST, the goal time is the problem, not you.

2. BLOCK RAMP
   4-week average volume, block over block. Flag anything >20%.
   Runna: +20%, +16%  |  Garmin: +16%, +11%

3. HARD TIME SHARE
   Minutes at or above threshold / total weekly minutes.
   Target 8-15% for marathon, 10-20% for 5K/10K.
   Runna wk9: 19%  |  Garmin wk9: 7.5%

Any single flag is fine. Two together in the same fortnight (a >20% ramp landing in the same week as a >18% hard share, say) is the pattern that precedes most self-inflicted injuries in AI-built plans.

The week 4 checkpoint

Don’t decide between these two on the strength of the plan preview. Run whichever one you’ve picked for four weeks, then do this: on an easy run, hold exactly 6:15/km for 40 minutes on flat ground and record your average heart rate and your decoupling (Strava shows heart rate for the run; split it in half and compare the two average HRs).

If your second-half HR is more than 5% above your first-half, at that pace, in week 4, your aerobic base isn’t absorbing the plan yet and the volume ramp is the thing to cut. If the two halves are within 3% and your average HR has dropped 4 or more beats since week 1 at the same pace, you’ve earned the next block as written, whichever app wrote it.