I picked up a Garmin Forerunner 255 last year,¹ and have kept a curious eye on its Training Status feature while training for a few races over that time. Unfortunately, I do not find it particularly useful. There are several significant problems with how it interprets training data in my experience to date.

First, over the same span, I also started using the 80/20 Endurance training plans, which emphasize an 80/20% mix of foundation work to higher intensity work.² Theoretically, Garmin’s Training Status feature ought to work really well with this. It breaks down your training load into one of three categories: anaerobic, high aerobic, and low aerobic. The anaerobic and high aerobic buckets should both map directly to 80/20’s high-intensity zones (X, 3, Y, 4, and 5), with the low aerobic bucket mapping to the low-intensity zones (1 and 2). In practice, the Training Status report gets very confused by the actual runs I do using the 80/20 plans.

As far as I can tell, this is because Training Status is designed to give every run a single score, and only breaks down the effect of the run between aerobic and anaerobic. That is: if you take a run that is a mix of sprint-type intervals and a long, slow warm-up and cool-down, Garmin might characterize that as contributing to both aerobic and anaerobic buckets. What it will not do is characterize a single run as contributing to both low and high aerobic buckets, even though many runs are designed to do just that. The 80/20 plans in particular nearly always include a mix of easy Zone 1 warm-ups and Zone 2 base mileage before switching over to tempo work, intervals, etc., and often also include a long cooldown. That kind of run is doing multiple things for your system in terms of physical performance, but Garmin seems to treat the whole run as “high aerobic” once it crosses some (relatively low!) percentage threshold of the run in Zone 3 or higher. Once it does that, the entire run is treated as increasing high aerobic load and high aerobic load only. The 80/20 plans incorporate foundation work into nearly every run, though, rather than having specific runs which are purely for speed or tempo work. Net, Garmin substantially mischaracterizes the runs in a way it would not if I broke them into three separate runs for the warm-up, tempo or interval work, and cooldown. I am not doing that because it would be a huge pain.³

Second, it is weirdly inconsistent about how it characterizes runs and rides. I regularly see it categorize an hour-long ride where I spent the whole time solidly in Zone 2 for power and much of it in Zone 1 for heart rate as a tempo ride. From time to time I have seen it do the same with long runs with similar heart rate and power zone breakdowns — including times where I have never even come close to the top of Zone 2 for heart rate. Despite the fact that power is all over the place — there is literally nowhere I can run around here that does not include 200+ feet of climb and descent, and keeping running power perfectly “in zone” on those kinds of hills is difficult to say the least — I have seen those results even on runs where I carefully kept my power output consistently in Zone 2 as well. I have repeatedly checked that the Garmin heart rate and power zones are set reasonably, but… it does not matter. This results in Garmin consistently mis-categorizing even more of my runs as being in its “high aerobic” bucket.

Finally, Garmin simply does not seem to adjust for the impact of things like temperature on performance. My Training Status reports have asserted that I am “Maintaining” or “Unproductive” since the start of January, despite the fact that I have made significant progress on benchmark exercises in ways that are really obvious to me. The reason? It has been really dang cold out, because I live in Colorado. Oftentimes, there has been snow on the ground which I have been dodging. I am “not improving” on Garmin’s estimation of my V̇O₂ max… because I am spending an enormous amount of my physical energy staying warm, carrying around a bunch of extra pounds of gear to help me literally not freeze, and dodging ice. It turns out that my runs under those conditions do in fact not get faster compared to a baseline of runs in beautiful 50 – 60º weather in mid-to-late fall. This is not weird; this is entirely to be expected. The same dynamic shows up in hot summer runs, where Garmin regularly interprets running slower to avoid heat exhaustion in 90º weather under a bright Colorado sun as a performance regression — when in fact careful heat acclimation often contributes to significant performance improvements once temperatures come down in the autumn!

I wish Training Status understood that many workouts have multiple phases to them. In many cases, much of the underlying data is already there, given I am using “structured workouts” which carry along automatic sectioning data. Likewise, I wish it adjusted for weather, and had the ability to supply information about conditions like ice and snow and slush⁴ — the first part of which is also already possible, since Garmin pulls weather data to associate with activities already! I wish, in sum, that Training Status were smart enough to be useful to me — but as of today, I just ignore it.