April Updates: A Proper Fitness Model, a New Status Page, and In-Chat Reports

Hey everyone!

April ended up being a bit of a rabbit hole. I set out to get a better handle on how the app tracks fitness, and three weeks of sports science papers later... here's where it's landed.

The rule throughout was to avoid just spewing out a million charts, and boil things down to a few key reports, that can feed into conversations with the coach.

1. A proper fitness model

This is the big one.

Pufferized now tracks your fitness across two dimensions: Power and Endurance. It still builds on the traditional CTL/ATL/TSB approach (originally based on Banister's 1975 impulse-response model), but rather than rolling every session into a single number, the app now looks at what each session is actually training — and attributes the load to the dimension it develops.

Each dimension has its own build-up and decay rate, grounded in published sports science. Power builds fast, fades fast. Endurance takes longer to build, but sticks around for much longer.

The practical result: you (and the Coach) get a much clearer picture of whether your training is working, and where the gaps are. You're not just "fit". You're fit for something.

There's a longer article walking through the model and the science behind it — a bit of a reference library of the relevant sports science if you want to go deep.

2. A redesigned status page

The status page has been rebuilt around the new model. You'll now see:

Dimension bars — where your Power and Endurance currently sit relative to your personal peak
A fitness chart — both dimensions over time, with the total layered on top, and future projections based on your plan
Power curve — out to 4 hours, with markers flagging where you're pushing your ceiling

Collapsed Power and Endurance status panels showing current values, 42-day trend, 90-day peak and a short AI read-out

Power panel with the Power Curve expanded, showing the full 4-hour curve with green ceiling-push markers

Per-section AI notes — short, specific observations from the Coach on what the data is actually saying
Holistic fatigue & form review — training load, sleep, HRV and resting HR pulled together with a plain-language read from the Coach on where you are

Fatigue & Form panel with AI notes above Training Load, Sleep, HRV and Resting HR tiles

The headline tiles now show your training split, weekly volume, and plan adherence instead of the old CTL/ATL/TSB numbers. Less abstract. More actionable.

3. Session feedback: RPE, notes, and proper celebration

How did that go? modal with a notes field and an RPE dropdown set to 9 — Almost impossible

When you mark a session as done, you can now record your RPE (how hard it felt) and add post-session notes — how the legs felt, anything unusual, whatever you want to capture.

These feed into every bit of analysis the Coach does, so a session review or status check now factors in not just the data, but how it actually felt. Weird how much that changes things.

Session feedback card titled The plan didn't survive contact, with ride stats and Endurance and Power dimension deltas

The session feedback card itself has also had an overhaul. Responses are now magnitude-scaled — a recovery spin gets a quiet nod, a legitimate monster of a session will result in the coach becoming completely unhinged. If you actually win a race, you unlock something utterly ridiculous. No more identikit "GOOD SESSION" for an 8-hour day in the hills.

4. In-chat reports

The Coach chat showing a /review me command with a rendered Athlete Review report

One of my favourites. You can now generate proper rendered reports directly in the Coach chat:

/review session — pick a session, get a full breakdown: ride stats, dimensional impact, intervals, PBs, durability markers, and coaching notes
/review plan — a structured assessment of your current plan, with compliance tracking and where you sit on the fitness curve
/review me — a full athlete profile, phenotype and all, right in the chat

These render as proper structured reports rather than a wall of text you have to watch get painfully typed out. The idea is they're conversation starters: read the report, then ask the Coach about anything that jumps out.

5. The small stuff

A few other things that shipped:

Weekly log — now shows 9 weeks at a glance, with each week labelled against its training block. Easier to see where you are in the bigger arc.
Durability markers — peak efforts deep into long rides now get flagged in session reviews. Useful for anyone whose event is measured in hours rather than minutes.
PB detection — session reviews automatically flag personal bests across the power curve
LTHR setting — you can now set your lactate threshold heart rate in settings, which feeds into the Coach's analysis and training guidance
Duplicate ride cleanup — if you sync via both Strava and Garmin, the app now detects and handles duplicate activities properly. You can ignore or restore duplicates from your activity history.

What's next

Exporting sessions as workouts for Garmin and other apps is still the big one on the list, alongside automating some more coaching emails - so that you can choose a cadence that works for you.

Also... there might be a bit of a rebrand brewing over the next month or two... ;)

As always, please do get in touch with any feedback.

Cheers,
Angus