Claude as a personal trainer: a Project prompt or a connected log

There are two honest ways to turn Claude or ChatGPT into a gym coach. The first is a Project with a good system prompt, and it costs nothing beyond the chat you already have. The second connects the assistant to a workout log it can read and write. This page compares them fairly, gives you a system prompt that works on its own, and is specific about the point where the first route starts to cost you more than it saves.

Updated: 2026-09-16

The two setups side by side

Neither is the right answer for everybody. The rest of the page is the detail behind each row.

Route one: a Project with a system prompt

Both Claude and ChatGPT have Projects: a folder of conversations that share one set of instructions and a few reference files. For training that gives you a coach with a stable personality and a stable brief, without repeating your goal, equipment and injuries in every new chat.

1. Create a Project and call it something like Training.
2. Paste the system prompt below into the Project instructions, and fill in the part about you.
3. Add your current plan as a file, if you have one.
4. Start one new conversation per week inside the Project, and paste that week's sessions into it as you go.

The last step is the one that decides whether this keeps working, and the section on where it breaks explains why.

A system prompt to copy

This prompt is written for the Project route, so it works without any connector. Replace the lines in the ABOUT ME block with your own details.

You are my strength and conditioning coach. Your job is to plan my training,
keep it progressing, and adjust it when life gets in the way.

ABOUT ME
- Goal: build strength and some muscle
- Experience: about one year of regular training
- Schedule: 3 sessions a week, 60 minutes each
- Equipment: commercial gym
- Injuries or limits: none right now

HOW TO WORK
1. Before you plan anything new, ask about whatever in ABOUT ME is missing
   or out of date. Ask at most three questions at a time.
2. Plans are tables: exercise, sets x reps, weight in kg, rest.
   Give a starting weight for every loaded exercise, or say how to find it
   in the first session.
3. When I paste a session, restate it as a table first, so I can correct
   your reading before you draw conclusions from it.
4. Base the next session on the most recent logged numbers, not on a
   template. If a number is missing, ask for it instead of guessing.
5. Progress one variable at a time: reps within the range first, then load.
   If the same lift stalls for three sessions, say so and suggest one change.
6. Keep answers short. Explain the reasoning only when I ask why.
7. If I mention sharp pain, stop planning that movement and tell me to see
   a professional.

WEEKLY REVIEW
When I write REVIEW, summarise the week from the sessions in this
conversation: what was done, what moved, what stalled, and the plan for
next week as a table.

Three details in it matter more than they look. Restating the pasted session as a table catches misreadings before they become advice. Asking for missing numbers stops the assistant filling gaps with plausible guesses. And the weekly review gives each conversation a natural end, which is what keeps any one thread from growing without limit.

What the Project route does well

For planning, it is genuinely good. A modern assistant writes a sensible program when it knows your goal, schedule, equipment and history of injuries, and a Project means you state those once. It explains its choices when you ask, rebuilds a session when the rack is taken, and adapts a published template to the week you actually have.

It also costs nothing extra and needs no account anywhere else. If you train a few months at a time, log loosely, and mainly want a thinking partner for the plan, this route may be all you need.

Where the Project route breaks

The problems are all about the record, and they arrive slowly, so they show up weeks in rather than on the first day.

There is no durable, structured log. Your history is spread across chat threads, as text, in whatever words you used on the day. The Project file with your plan does not update itself after a workout. The assistant reads that file; it does not rewrite it. Keeping it current is a job you do by hand, and it is the first job people stop doing.

Every number is recalculated from scratch. Ask for your best squat, your weekly sets for the back or an estimated one rep max, and the assistant derives it again from whatever text it can see. Two conversations can give two different answers, and nothing marks which one was right. Arithmetic over dozens of pasted sets is exactly the kind of task a language model gets slightly wrong while sounding certain.

Context runs out. A long thread eventually holds more than the model can keep in view at once, and older detail gets summarised or dropped. A year of training at three sessions a week is roughly 150 sessions and a few thousand sets. You can split it into weekly threads, but then no single conversation can see the trend.

Built-in memory does not fill the gap. Both assistants can remember facts about you across chats, and that is useful for preferences like training four days a week. It is not designed to hold hundreds of sets with their weights, and you cannot chart what it stores.

The gym is the wrong place to type. Logging set by set in a chat between sets is possible and tiring. Most people end up writing the session from memory afterwards, which is where reps and weights go missing.

Route two: connect the assistant to a workout log

The alternative keeps the assistant you already use and gives it somewhere to write. Assistants connect to external tools over MCP, and AIm is a workout log built for that: a place your own Claude or ChatGPT reads from and writes to. The thinking stays with your assistant. What changes is what it has to work with.

• The log is written for you. Describe the session in a sentence, and the assistant saves it as records: exercise, set, reps, weight. Correct a set the same way, or with the edit button next to it in the app.
• The coach reads before it plans. When you ask for the next workout, the assistant reads your goal, equipment, injuries and recent sessions from AIm first, so the plan starts from last week's numbers, in a brand new chat.
• A workout screen for the gym. Your program sits on the Workouts tab. Start a day and the screen shows each exercise with its target, what you did last time once there is a record, and a rest timer after each marked set. Finishing saves the session to the same log the assistant reads.
• Numbers computed once, the same way. The Progress tab calculates progression, personal records and an estimated one rep max with one fixed formula over every logged set, so the answer does not depend on which conversation you ask in.
• Your data leaves when you want. Export the history as an Excel file or as JSON.
• One log for both assistants. Claude and ChatGPT can connect to the same account, so switching assistants does not split your history.

Setup is a free account and one address, aim-journal.com/mcp, added as a connector. In Claude that works on the free plan. In ChatGPT, adding a connector needs Developer mode, which is on the paid tiers.

What AIm does not do

• Planning is your assistant's job. The program, the explanations and the advice come from Claude or ChatGPT. AIm keeps the record and does the arithmetic on it.
• It does not watch your technique. Nothing that reads text or numbers can see your knee cave on the third rep.
• It does not sync from other devices or apps. Workouts arrive by telling your assistant or by using the workout screen. History from another app comes in as a file the assistant reads.
• It does not track food. The log covers training, body measurements and goals.
• It does not remove the need to check. The assistant structures what you say, and a misheard number is still possible. Every saved set is visible in the app and fixable.

Keeping the system prompt after you connect

The two routes combine well. A system prompt sets the coaching style; a connected log supplies the memory. With AIm connected, the prompt above gets shorter, because the steps about pasting sessions and restating them are no longer your job:

You are my strength coach. Keep answers short and explain only when I ask why.
Before planning a workout or reviewing my week, read my training data from AIm.
When I describe a session, log it to AIm, then confirm what was saved.
If a number is missing, ask for it instead of guessing.
If I mention sharp pain, stop planning that movement and tell me to see a professional.

Your goal, equipment and injuries do not need to be in it. The coach profile in AIm holds them, and the assistant saves changes there as you mention them.

Which route fits you

Stay with the Project if you mostly want help writing a plan, train in blocks of a few weeks, and do not look back at old numbers. It is free, it is private to your assistant account, and the prompt above makes it a good coach.

Connect a log if you want progression to rest on what you actually lifted, if you have caught yourself retyping history into a new chat, or if you want to record sets in the gym on a screen made for it rather than in a text box. The honest test is simple: if keeping the Project file current has already slipped once, the record is the part that needs fixing, and a better prompt will not fix it.