Muscle Diary is a simulation game where you plan a pixel-art character's training week, food, and sleep, then see how strong they can get in 12 weeks (84 days). This page explains how to play, how to read the screen, and the events that can happen in the game. For how muscle and lifts are calculated, see How the Math Works.
1. Create your character
On the first screen, choose your character's sex, height, weight, age, body fat, lifting experience, and job.
- The starting values are typical U.S. adult averages for height, weight, and body fat. Switch the sex and they change to that sex's averages.
- Choose your lifting experience from "Brand new," "Under 6 months," or "1 year or more." The newer you are, the faster you build muscle, and the more your lifts jump in the first few weeks.
- Your job sets how active you are during the day (activity level), which is used to calculate calories burned.
- At the top of the screen, you'll see your character's body type along with lean mass, body fat, FFMI (fat-free mass index), and BMR.
2. Enter your current lifts
For the bench press, squat, and deadlift, choose a weight and how many reps you can do with it. The game uses that to estimate the most you could lift for a single rep (your one-rep max, or 1RM).
- Not sure? An estimate based on your weight and experience (a weight you could lift for 5 reps) is already filled in.
- If you change your sex, weight, or experience, the estimate updates too, as long as you haven't changed the lifts yourself.
3. Set a goal
Pick one of three goals and set a target.
| Goal | Choices |
|---|---|
| Bench press | Heavier than your current 1RM (in 5 lb steps) |
| Body fat | Lower than now (down to 8% for men, 15% for women) |
| Build muscle | How much lean mass to add (1–13 lb) |
If your goal looks hard to reach in 12 weeks, you'll see a note. You can still go for it.
4. Plan your week
In "Weekly plan," choose a muscle group and an intensity for each day of the week.
- Muscle group: Rest, Chest, Legs, Back, or Full body. Chest raises your bench press, legs your squat, and back your deadlift. Full body trains all three a little.
- Intensity: Light, Normal, or To failure. Harder sessions give your muscles more stimulus, but also build up more fatigue.
- How much you eat: Cut (−500 kcal), Maintain, or Bulk (+300 kcal). Cutting burns body fat, but makes it harder to build muscle.
- Protein: Low (0.36 g per lb of body weight), Enough (0.73 g/lb), or Plus shake (1 g/lb). Going above 0.73 g/lb doesn't make muscle grow any faster.
- Sleep: 5, 7, or 9 hours. Short sleep slows recovery from fatigue and makes muscle grow more slowly.
Below the plan, you'll see today's workout, calories in and out, your daily protein, and your "weekly stimulus." Weekly stimulus is a guide that comes out to 6 when you train each of the three muscle groups twice a week at Normal intensity. Too little or too much isn't efficient.
You can change your plan at any time, even in the middle of the game.
5. Start training
Press "Start training" and the days move forward automatically. You can choose from three speeds.
| Speed | Time per day | Time for 12 weeks |
|---|---|---|
| Slow | 1.5 sec | about 2 min |
| Normal | 0.5 sec | about 42 sec |
| Fast | 0.2 sec | about 17 sec |
Press "Pause" to stop, adjust your plan, and then "Resume." There are also speed and pause/resume buttons under the status panel.
6. Reading the screen
- Day: which day you're on (up to day 84, or 12 weeks) and which week
- Weight, lean mass, body fat: current values and the change since you started. Lean mass is your weight minus body fat
- Bench press, squat, deadlift: your current one-rep max (1RM) and the change since you started
- Fatigue: fatigue in your most tired muscle group (0–100). Injuries and colds also show up here
- Motivation: when it's low, you're more likely to skip workouts
- Goal: how far you have left and a progress bar
The chart can switch between 1RM (all three lifts), lean mass, body fat, and weight. Charts that match your goal show a goal line.
7. Events in the game
| Event | When it happens | Effect |
|---|---|---|
| Fatigue | When you train the same muscles without rest | Training a tired muscle gives less stimulus (half at fatigue 50) |
| Injury | When you train "To failure" and that muscle's fatigue goes over 80 (8% chance) | You can't train that muscle for 7 days, and motivation drops |
| Plateau | When you keep the same plan for 4 weeks | Stimulus drops a little. Change your plan to get it back |
| Personal record | When your 1RM passes the next 5 lb step | Motivation goes up |
| Soreness | The day after a "To failure" session (30%) | Motivation drops |
| Night out | Now and then (more often on Fridays) | +1,200 kcal, and you sleep 1 hour less that night |
| Packed gym | Weekday training days (8%) | Less stimulus that day |
| Skipped workout | When motivation is low (more often on weekends and rainy days) | No training that day |
| Cold | Now and then (2%) | No training for 3 days |
8. Your 12-week results
After day 84, you'll see your character at the start and after 12 weeks side by side, along with changes in weight, lean mass, body fat, and your 1RM on all three lifts. You can share your results on X or other apps.
If you reach your goal before then, you'll see "Goal reached!" that day, and the game keeps going until week 12.
Press "Back to Day 1" to start over with the same character and plan. Press the title at the top of the screen to go back to the first screen and create a new character. You can pick up your previous game with "Continue."
How your data is saved
What you enter and your game progress are saved only in your browser. Nothing is sent to a server. If you clear your browser data, your progress is deleted too.