"Train or rest today": three Polish riders turned "paste your screenshot into ChatGPT" into a $15/month AI coach

RestOrTrain is a chat-only AI endurance coach. It connects to your Garmin and Intervals.icu, reads all your training and recovery data itself, you ask what to train today, it answers, and then it pushes the workout to your bike computer. The iOS version ran for a year and passed 50k registered users; in Sep 30 it launched on Android, and about 33k installs came in five weeks. It didn't invent a new category, and the niche is already crowded. What's worth looking at is the approach: it packaged something users were already doing by hand, and it priced it high.

An Ironman athlete who could only use it on an iPad

In 2026 Jul 16, Martin Buchholz, a triathlete, left a comment under a thread on the official Intervals.icu forum. Before, he fed his training data to AI by uploading .FIT files, CSVs and screenshots over and over, because hooking up the API himself was too much work. With RestOrTrain all that went away. He also wrote: "I am an Android guy, so I am stuck using only on my iPad." He uses an Android phone, so he was stuck with the iPad.

In Sep 30, RestOrTrain co-founder Michał Michalik replied in the same thread: the Android version was out, and he even tagged Martin by name. That same day Martin replied: "Just downloaded and it's up and running. It's great!" A month later he came back with a request: he was training for a full-distance Ironman and wanted the coach to help him compare new running shoes, but the app couldn't take video uploads or links. The founder replied, adding "glad the pacing plan in Nice helped."

That thread was started in 2026 Apr 8, with a self-deprecating title, "yes, another one..." (yep, another AI coach). By November it had 2,895 views and 24 replies. You can get a rough sense of how RestOrTrain took off from this thread.

What it is

The whole app has three parts: chat, calendar, and profile. No dashboard, no charts. Co-founder Antoni Szczepanik said in a post that Intervals.icu already does charts well enough, so they aren't competing on that.

Here's how it works: connect Garmin, Intervals.icu, Wahoo, COROS, Hammerhead and other data sources, and it syncs your full ride and run history, plus HRV, sleep, resting heart rate and weight. Then you just ask: "look at this ride for me," "should I adjust the power target in this workout next time," "what did I train before my best-ever power." You can also have it plan a week of workouts or a whole season. Finished plans are written back to the Intervals.icu calendar and pushed to devices and platforms like Garmin, Wahoo, Zwift and ROUVY. By September it could remember what you'd told it before, would send an observation after each ride, and sent a daily training briefing in the morning. The app has 7 interface languages, and the coach can answer in 21 languages.

The selling point it keeps stressing is "AI only interprets". Fitness (CTL), fatigue (ATL), form (TSB), heart-rate and power zones are calculated first with fixed formulas, then handed to the model. According to the founders, the model's job is to read those numbers, not make them up. Their website also notes that models tend to prescribe weeks that are too easy, and they tuned for it specifically.

Three people in Kraków built it: Antoni was previously a software engineer at Google; Michał is a former Polish national alpine ski champion and is also an engineer; Wojtek previously worked at EY.

How much it grew

For comparison, in the same week, rating growth on iOS was 166 for RestOrTrain, 0 for the veteran TrainerRoad, and 13 for JOIN.

Where the money comes from: free gets 10 messages

The free tier gives roughly 10 messages a month, enough to plan a week of workouts or check a few rides. After that you have to subscribe to Pro: $14.99 a month or $134.99 a year in the US store (Google Play in-app prices). When they posted in April, it was $12.99 a month, and the Canadian-dollar price is now 22.99.

The founders spelled out the logic on the forum: they regularly test which model is the best cycling coach and use that one, which costs real money, so the full version is paid. The price is aimed at heavy riders, who are used to spending money: a bike computer costs hundreds of dollars, a power meter over a thousand, and a human coach runs a hundred or two a month.

The price draws opinions from both sides:

"I used to pay a lot for a cycling coach, and this app is just as good, or better." (App Store US, 07-14,5 stars)

"Used up the free messages in 5 minutes, and it wants me to upgrade to Pro or wait 30 days. Didn't even finish a training plan, deleted it right away." (App Store US, 08-01,1 stars)

A Google Play user made a practical suggestion: once the free allowance runs out, could you watch an ad for one more question (10-08).

Where users come from

Pent-up Android demand, released all at once. This is the main reason the Android numbers look good. iOS ran for a year first, and Martin, the Android user making do on an iPad, wasn't the only one on the forum. Pre-registration opened in Sep 16, the launch came in Sep 30, and about 27k installs came in the first month, roughly matching "50k registered users, some of them waiting for Android" (my guess).

The founders work the community themselves. Intervals.icu is the free training analysis site nearly every serious endurance athlete uses, and its official forum is where these people gather. The two founders reply to bugs one by one in threads and announce new features, and they also post in a Facebook group for MyWhoosh (indoor cycling software), and started an r/RestOrTrain subreddit where they post changelogs. On Reddit's r/Velo and r/cycling, people ask "which AI training app is good," and it keeps getting recommended in the replies.

Launch week, press went out together. On Sep 20, the cycling review site the5krunner ran an "Indie Spotlight" written by co-founder Michał, edited by the site; on the day Sep 30 launched, the industry site endurance.biz published a press release.

SEO, all at once. From mid to late September the site published a batch of pages: "Best AI Cycling Coach Apps of 2026", "How to Choose an AI Cycling Coach", "Free AI Cycling Coach", "How to Use ChatGPT as a Cycling Coach", plus head-to-head comparison pages against TrainerRoad, JOIN, ChatGPT and a dozen similar tools. Search "AI cycling coach" on Google and its own ranking and comparison pages come first. Now that many people ask AI directly, these pages also get cited by AI search as sources.

Short video is being tested, volume is still small. The YouTube Shorts channel "rest or train!", opened Aug 31, has posted 69 videos with 34k total views and 23 subscribers. The copy is amateur-style hooks like "Never paying for a cycling coach again", "Strava + Garmin + Claude = RestOrTrain", "Comment \"HOW\"", plus an Italian version. The TikTok account has 223 followers. Five or six cycling YouTubers have also reviewed it, each getting one to four thousand-plus views, one with a promo code. These don't bring in many users; they read more as endorsement.

Whether it's paying for ads can't be seen from outside. The website's download links carry attribution parameters; its iOS ratings are high in South Africa, Brazil, Colombia and the Philippines, which is a lot for a Polish cycling app. That could be from paid acquisition, or simply because many people ride in those countries (unverified). On Google Play, the rating count is roughly 4% of installs. On some days installs didn't move but ratings still rose by a dozen or two a day, most likely a rating prompt shown after the app delivered a good result in conversation (inference).

Why it keeps people

The clearest evidence is a line from Rod Roederer on the forum in Nov 5:

"I used to use ChatGPT and had to copy intervals.icu screenshots and download csv files for ChatGPT to analyze. Now it's all automatic."

Endurance athletes were already using ChatGPT as a coach, but they had to feed it data by hand every time. RestOrTrain turns that workflow into an app, and the name is the question riders ask themselves every morning. It adds three things over asking ChatGPT directly, and these are the reasons users pay:

1. Data comes in on its own, no screenshots;
2. The numbers are calculated, not guessed by a model, which heavy users care about most;
3. Workouts push straight to your head unit. ChatGPT can tell you what to ride today; RestOrTrain can put that session on your Garmin.

Timing helped too. In 2026, the veteran TrainerRoad launched an AI version with mixed reviews, and Strava stopped opening its data to third-party AI, leaving its own AI to summarize single activities only. One iOS review (09-13) said: "I've used all three, only RestOrTrain looks at your whole history." RestOrTrain skipped Strava and pulled data from Garmin and Intervals.icu instead.

Users also complain about a few clear things: some say it "always gives Z2 aerobic and only one interval session" and is "just another garbage AI" (09-19); some say it "rewrites the plan almost every day and forgets what it changed" (Google Play, 10-16); some say it's no different from using Claude directly (07-01); and a harsher one: "Writing good prompts takes coaching-level training knowledge, and people with that knowledge don't need it" (08-15). In the chat-coach category, these are problems every product eventually runs into.

Who it's competing with

There are a lot of competitors.

New same-generation rivals are already writing pages aimed squarely at it, which shows that within the small AI-cycling-coach circle it's the one others are chasing. Its lead is only three things: it launched six months to a year early; it supports cycling, running, swimming and triathlon; and it connects the most data sources and devices (9). All of these can be caught up with.

If it were you

C. Don't build "another AI cycling coach": there are over a dozen here already, and rivals are writing pages to capture its traffic. What's worth learning is how it found its opening and its launch playbook.

Who it suits: Heavy users of a sport or serious hobby who know what data people in the scene are currently pasting into ChatGPT, and which APIs that data comes from. Able to write mobile code and to handle integrations with three to five devices or platforms yourself.

Who it doesn't suit: Anyone wanting to head-on into cycling or running (TrainerRoad and Runna have big-company resources, and there are plenty of RestOrTrain-style same-generation rivals); anyone not willing to show up in the community long term and reply to posts daily; anyone who can't afford model costs and can only rely on free plus ads (this audience wants accurate answers, and a downgraded model loses them).

How to build it: Pick a vertical where users are already manually feeding ChatGPT. I checked a few adjacent sports: HYROX, climbing and powerlifting already have AI coaches, and they all appeared in the last 2025 to 2026 years, so before you pick, count how many players there are and how big they've gotten. Once you've picked, follow its three rules: pull data in automatically; compute the metrics you can calculate deterministically first, with the model only interpreting; and write results back to the devices or calendars users already use. Make the interface chat. Name it with the question users ask every day. Keep the free tier small and price it at $10 to $20 a month based on model cost.

How to get users: Find the core forums, groups and subreddits of the community, have the founder post personally with "another one, but here's what we got right", and fix bugs in replies one by one. Run word of mouth on one platform first; when opening a second platform, use pre-registration to build a list; in launch week, release the review site article, community posts and SEO pages together. Publish the SEO pages all at once: "Best X ranking", "X compared to every competitor", "Free X", "How to use ChatGPT for X".

When to get in before: There's no hard deadline. The AI coach wave has been emerging across many sports at once over the last 2025 to 2026 years, and a niche usually has a half-year to one-year first-mover window. Once three or more players are publishing comparison pages in a niche's "AI coach" search results, you're late.

What would show I got it wrong: (1) RestOrTrain's Google Play installs hold at 5,000+ per week after the launch buzz fades, and the iOS US store reaches the top 50 of its category's top grossing. That would mean the cycling market is bigger than it looks and there's room to compete head-on, so the grade should go up. (2) Conversely, if Garmin or Strava ships a native AI coach that reads your full history and builds and pushes workouts, this product's advantage of automatic data access disappears overnight, and building in another sport is just as risky.