I Built an AI Personal Trainer That Checks In on Me (2026)

I was an online PT for 2 years. My clients could have got a training plan and a meal plan anywhere. What they paid me for was accountability, positivity and motivation: someone checking in, noticing when they drifted, and keeping them going on the days they didn't fancy it.

These days ChatGPT writes the plan in ten seconds. But ChatGPT never messages you first. So I built an AI personal trainer that does.

It lives on my Mac mini, talks to me on Telegram, and it's what has kept me consistent.

Can AI be your personal trainer?

For most of the job, yes. Any of the big models will write you a solid programme, work out your calories and swap a meal when you're sick of chicken and rice.

What they can't do on their own is chase you. A chatbot waits in an app until you open it, and the day you most need a nudge is the day you don't open it. That's the gap people still pay a coach to fill, and it's the bit I wanted to automate.

What my AI personal trainer does

It runs on a schedule and messages me in Telegram, the same way a coach would on WhatsApp:

• 7pm every day: "Green, Amber or Red?" Green means I hit my calories, Amber means close, Red means it went wrong. I reply with the colour and roughly what I ate, and it keeps a running tally and my streak.
• Wednesday and Sunday mornings: it asks for front, side and back photos. It compares them with its notes from last time, gives me a visual body fat range and sets one thing to focus on until the next check-in.
• Tuesday and Saturday evenings: a short nudge that photos are due in the morning.

On a Red day it doesn't lecture. It asks what triggered it and agrees one fix for next time, then writes both down. It keeps a log of every check-in, so it can spot patterns across weeks instead of judging one day on its own.

Why the night before photo day works

Late-night snacking is my big weakness. I'll have a great day and then undo it at 10pm on the sofa.

The 7pm check-in fixed most of that, because I don't want to type "Red" into my phone. The bigger surprise was the photo days. Tuesday and Saturday used to be my worst nights. Now I know the camera comes out the next morning and the coach is going to compare the photos, so I don't cheat on those nights. It's the same thing my online clients paid me for.

How it works

There are three parts:

1. Hermes Agent is a free, open source AI agent from Nous Research. It runs 24/7 on my Mac mini. It works just as well on a Windows PC that stays on or a cheap Linux server.
2. Gemini is the brain. I use Google's model because it's good at looking at photos, which the body fat check-ins need. Any model that can see images will work.
3. Telegram is how we talk. It's a free bot only I can message.

I didn't write any code or config files for the coaching. Once Hermes was connected to Telegram, I set the rest up by messaging it: my goals, my targets, how I wanted to be coached and when I wanted the check-ins. It saved my goals to its memory, wrote itself a routine for running check-ins, kept a log and set up the scheduled messages on its own.

If you've used any of the AI tools I rate for running a business, the difference is that Hermes runs on its own schedule. You don't have to remember to open it.

Can AI estimate body fat from a photo?

It gives a range, not a number, and I told it to always say so. Lighting, pump and the angle of your phone all change how a photo looks.

The range is still useful for the trend. Same mirror, same light, first thing in the morning, twice a week, and over a month you can see the direction clearly. It compares each set of photos against its written notes from last time, not against how you feel about yourself that morning, which keeps it honest.

If you want an exact figure, a DEXA scan is the way. For staying on track week to week, the photos are enough.

What it costs

• Hermes Agent: free.
• Telegram: free.
• Gemini: billed per use. For one check-in a day and two photo reviews a week, it's roughly £1 to £5 a month depending on which model you pick.
• The computer: my Mac mini was already on 24/7 for other jobs, so it's just electricity. A small server works out at around $5 a month if you don't have a spare machine.

When I was coaching online I charged £200 a month, and most of that was for the accountability. This does that part for a few pounds.

Will AI replace personal trainers?

For online coaching, a big chunk of it, yes. Plans and macros were already free, and accountability was the main reason my clients paid me. Now the daily check-in is free too.

The coaches who'll be fine are the ones teaching technique in person and the ones people stay with for the relationship. A good PT spotting your deadlift is still worth every penny. Paying monthly for someone to ask whether you hit your calories is harder to justify.

What else can Hermes Agent do?

The same setup (memory, a routine it writes for itself, a few scheduled messages and a Telegram chat) works for anything you want to be held to. A daily brief of your calendar and inbox. A reminder to invoice on the last Friday of the month. A reading or study habit with a streak. Once it's set up, adding another is one message.

If the idea of a computer that runs jobs around the clock is new to you, my post on running n8n in the cloud or on your own server covers the same trade-off from a different angle.

Get the full setup

The complete guide takes about 45 minutes. It covers installing Hermes on a Mac, Windows or a Linux server, connecting Gemini and Telegram, and the exact setup message to send your bot so it builds the coach, the memory and the check-in schedule for you.

Questions people ask

Can you use AI as a personal trainer?

Yes, for most of what a PT does. The big models will write a training plan and a meal plan in seconds. To get the accountability part you need an agent that runs on a schedule and messages you first, which is what this setup does.

Is there a free AI personal trainer?

The software is free: Hermes Agent is open source and Telegram costs nothing. The AI model is what you pay for, roughly £1 to £5 a month for a coach like mine, plus a computer that stays on.

Can AI estimate body fat from a photo?

It can give a visual range and track the trend over weeks. It isn't a measurement, so take photos in the same place and light each time and treat the number as a guide.

Will AI replace personal trainers?

A lot of online coaching, yes. In-person coaches who teach technique and build real relationships will still be worth paying for.

What is Hermes Agent?

A free, open source AI agent from Nous Research that runs on your own computer or a server, connects to models like Gemini, Claude or GPT, talks to you on Telegram and runs jobs on a schedule.

This isn't medical advice. If you have a health condition, an injury or a history of disordered eating, speak to your GP before you start a cut.

Mike McDonnell. I write The Growth Toolkit, a free Sunday email on freeing up time with better tools, AI and setups.