The target is calculated.Not generated.
You walk up to the machine and the next number is already there — worked out from what you last lifted. Load, recovery, volume and progression come from an engine, and the same input gives the same result every time. The language model puts that into sentences and talks to you about it. It invents no number.
The iPhone app is in closed beta. In the browser Cox runs today — on iPhone, Android and desktop.
Mid-session. Example data.
In the gym your phone lies face down on the bench.
Which is why Cox Strength is a real app and not a website wearing one. Three things a browser cannot do — and you need all three between two sets.
The rest timer runs on the lock screen
In the Dynamic Island and on the locked display: time left, next exercise, how many sets remain. It counts down from a date range rather than being pushed a new value every second — so it stays right while the app is long asleep.
No signal, no problem
Before you leave, the app pulls a supply: today's plan, your last weights, the targets, the movement clips for the exercises you have planned. In a basement with no reception you log normally; whatever hasn't reached the server waits and goes out later.
Heart rate from the belt, gym from your location
Cox pairs with your chest strap directly — over the standard Bluetooth service, not a brand list that goes stale. And when a session starts it asks once where you are, to pick the right gym: the machine standing there has its own progression.
The rest timer keeps running while you are in a completely different app. Example data.
One session, start to finish.
Not a tour of menus — the path a training day actually takes, and for every step, where the number in it came from.
In the morning, what's on today
The session of the day, your strength score, how your trend is going, what you have eaten, where your weight sits. Above it a line about your readiness — with the measured reason next to it, not a phrase.
If nothing was measured, nothing is claimed. A number with no measurement behind it would be an assertion about your body, and none is used here to fill a gap.
The day on one screen. Example data.
No routine in mind? Cox works one out
"Compose a session" builds a proposal from where your training stands: what came up short this week, what is long overdue, what still has room. Every exercise in it says why it is there — "last trained 18 days ago", "below your weekly landmark".
You get several proposals at once, not one after another. Gyms often have no reception, and a "give me another" that needs a reply from the server is exactly the control that fails there.
A proposal, with its reasoning. Example data.
At the machine, the target is already there
Weight and rep window for this set, and beside it what you managed last time on this machine. Under it the method in plain words: "double progression: next step 170 kg, back down to 4 reps".
The number in the field is the bottom of the range — the one you are meant to beat. That is why the whole range sits above the column and not only in the card header.
Target, range, last performance. Example data.
Between sets the clock runs — and so does your pulse
Ticking a set starts the rest; its length belongs to the exercise, not to one number for everything. A sound tells you, even with the display off, because it is scheduled as a notification rather than hanging off an open screen.
Wear a belt and your heart rate runs alongside and travels into the saved session. Any standard sensor shows up in the list — including a Garmin watch in broadcast mode.
Heart rate from the belt, live. Example data.
When something doesn't work, Cox proposes — it does not decide
Machine taken, back complaining, no time: you give the reason, and the replacement comes from the same movement pattern — closest match first. The reason travels into your history, so nobody later wonders why that day looks different.
Four mechanisms are allowed to argue with your numbers: readiness, interference from endurance work, a deload week, an assumed unloading. All four propose — as a note on the exercise, with the exact sentence a tap away. What gets applied is what you confirm; otherwise you could no longer explain your own number.
Swapping, with a reason. Example data.
At the end Cox adds it up — and asks
Sets, tonnage, duration, heart rate. If an exercise went better than ever before, it says so, worked out from weight and reps. Plus a field for a note, and underneath it says who reads it: your coach.
A finished session advances the rotation; an abandoned one does not. Abandon it and you lose nothing but the session — the progression is rebuilt from what remains.
Finishing, with a note to the coach. Example data.
Later, the map tells you where you stand
How many hard sets each muscle group got, measured against your bands — not a table for everyone. Where it was too little, where it fits, where it is becoming too much.
The bands depend on everything else you do: someone who runs and rides alongside the gym tolerates different amounts than someone who only lifts.
The week on the muscle map. Example data.
Two separate jobs: calculating and phrasing.
A language model that invents training plans answers differently on two days with nothing changed. For progression across weeks that is useless. So code does the arithmetic here, and the model receives the result.
Every number opens up
No score nobody can recompute. Tap your readiness and it falls apart into the values it is made of — each one saying how far it sits from your own average and how much it counts.
Underneath, where the numbers came from: which device, which service. What wasn't measured isn't substituted, it is left out.
- Same input, same result — the same formulas, every time
- Your thresholds are yours, measured against your own baseline
- Every progression method names its source, with author and year
One number, opened up. Example data.
Strength is the way in.
Nutrition joins when you need it. The coach sees both.
Strength
Four progression methods, each with its source. The target goes up when you make it — and when nothing has moved for weeks, you get a proposal instead of a shrug.
Take a lookNutrition
Photograph the label and the numbers are there. The model reads, the code does the maths. Balance, protein per meal, carbs around the hard session.
Take a lookThe coach
It phrases what the engine worked out, remembers what you tell it — and proposes changes to your plan rather than applying them.
Take a lookBy the third month it knows you better than in the first.
A coach that starts from scratch every session is a chat window. Cox builds a picture of you over weeks — and measures itself by how rarely it has to interrupt you to do it.
It gets to know you
That Tuesdays never work, that your back has opinions about heavy squats: at most one question a day, from the area it knows least about. What you mention in passing counts the same — it never asks twice.
It writes first
A briefing in the morning for what's ahead. After a session a follow-up that knows which session it was. The week on Sunday. And when three sessions on the bench move nothing, it says so.
And it holds back
Every unprompted message clears five hurdles: quiet hours, one topic a day, a minimum gap, a daily limit, and it waits on an unanswered question. What it wants to change in your plan it proposes — applied once you agree.
This engine was not built for a product page.
It has coached a single athlete every day since June 2025, on a machine in the next room. Strength is the part coming out now. It is not the whole.
The athlete first, the product after
Cox started as an endurance coach: load and recovery across months, weekly planning, race preparation, body composition, nutrition — grown around one person who trained with it every day. Much of it is still running there while you read this.
And then piece by piece
What becomes public arrives one piece at a time — and each only once it is clean for other people's accounts: your own data, your own thresholds, nothing bleeding through from the account next door. Strength and nutrition are first.
We name a date for none of it. What already runs and what is still outstanding is written out on its own page.
Who this is built for.
You've been lifting for two years and don't know whether you're getting better — your plan is a screenshot off the internet.
You log your sets into an app and get charts back. What you don't get is a call.
You've been stuck at the same weight for months and don't know whether the answer is more food, more sleep, or different training.
And what Cox is not for
- Cox is a wellness companion for your training — not medical advice and not a medical device. If something hurts or worries you, that belongs with a qualified person near you.
- Cox plans for people who already train. If you have no access to weights or machines yet, you are here too early.
- No points, no streaks, no leaderboards. Cox compares you with yourself, not with anyone else.
Where the data comes from, and where it stays.
No device required — strength and nutrition work with what you enter yourself. If you have a watch or a scale, the arithmetic gets sharper.
Strava is out: their API terms forbid processing third-party data with AI — for an AI coach that is not a question of effort but structurally closed.
And with no iPhone around, it runs in the browser
Cox is also a web app you add to your home screen — on iPhone, Android and desktop, notifications included. Planning, analysis, talking to the coach and logging food all work there in full.
What the browser lacks is exactly the gym part: rest timer on the lock screen, the heart-rate belt, Apple Health, and the supply that carries you through a basement with no signal.
The same session in the browser. Example data.
And where it stays
Servers in Germany, database in the Netherlands. Nothing sold, no advertising, no tracking pixel — which is why this page never asks you about cookies. Your training and body data is processed only with your explicit consent, and you can withdraw it at any time.
Every provider involved, the AI models included, is listed in full in the privacy policy.
Questions, answered briefly.
Can I download the app from the App Store?
Not yet. Cox Strength runs as a closed test through TestFlight and we invite people in batches — it goes to the store once enough accounts have run through cleanly. Join the waitlist and you get access as soon as a place opens.
You don't have to wait for it, though: the web app is open to every invited account and covers everything except what a browser structurally cannot do.
And if I'm on Android?
Then you use the web app — added to your home screen it behaves like an app, notifications included. Planning, analysis, logging food and talking to the coach all work in full; the heart-rate belt, the lock-screen rest timer and Apple Health are iPhone only. There is no Android app, and we name no date for one.
Is this a chatbot with my training data?
No. Load, recovery, volume and progression are worked out by an engine — the same formulas, same input, same result, openable step by step. The language model turns that into sentences and talks to you about it. It invents no numbers, and it doesn't decide what you train.
Do I need a watch or a scale?
No. Strength and nutrition work entirely on what you enter — sets in the gym, food by photo. If you supply sleep and recovery values the daily recommendation gets sharper; without them Cox plans anyway and leaves the line out rather than inventing a number.
Does the app work without a signal?
Yes, and it is built that way rather than by accident. Before you leave, the app pulls today's plan, your last weights, the targets and the movement clips for the planned exercises onto the phone. In the gym you log normally; whatever couldn't go out waits and is sent on once you have signal again.
What happens to my data?
Servers in Germany, database in the Netherlands. Your training and body data is specially protected — Cox processes it only with your explicit consent, which you can withdraw at any time. For the coach's replies your context goes to an AI model; which providers those are is listed in the privacy policy.
You delete your account yourself, in the settings. Before you do, Cox shows what hangs off it and which connected data sources get deregistered in the process.
What will Cox Strength cost?
Nothing during the closed beta. After that Cox becomes a paid subscription — strength as the way in, nutrition as a block you can add or leave. Prices aren't fixed yet, and nothing becomes payable without your explicit agreement.
Who is behind it?
Cox is built in Germany by one person. The engine is not a wrapper around a language model: it has run since June 2025 as one athlete's coach, before it became a product — the origin is written out. Who is responsible is in the imprint; questions go to [email protected] and are answered by a human.
Cox Strength is coming.
Closed beta: we invite people in batches. Leave your address and you'll hear first when a place opens.
Thanks — you're on the list.
You'll get a short confirmation by email in a moment. As soon as a place opens, we'll be in touch.