MuscleBuddy
AI fitness coaching that adjusts your program and nutrition automatically as you progress
Features
- •AI-generated training programs — splits, mesocycles, and deload weeks calculated from your schedule, equipment, and goals
- •Six progression methods including double progression, RPE, percentage, and wave loading
- •Automatic nutrition adjustment — TDEE via Mifflin-St Jeor, rolling weigh-in averages trigger calorie and macro changes without manual intervention
- •Food logger with 1000+ item knowledge base, custom foods, and full micronutrient breakdown
- •Coach tools with client management, custom program templates, and revenue share via Stripe Connect
- •Offline-first with IndexedDB and Workbox service worker — workouts and food logs sync on reconnect
What it is
MuscleBuddy is a fitness coaching PWA built on the premise that most training apps are either too simple to be useful or too complicated to stick with. It targets the full range from first-time gym-goers to competitive bodybuilders with a single codebase, using configuration to surface only what each user actually needs.
The core of the product is an algorithm-first engine. Progression calculations, TDEE estimation, macro targets, and nutrition auto-adjustment are deterministic rule engines — not AI. The Claude API handles conversational features, check-in analysis, and coaching explanations, but no core calculation depends on the LLM. This separation keeps the platform fast, consistent, and testable.
The tech stack is a monorepo: React 18 with Vite on the frontend, Fastify on the backend, PostgreSQL via Prisma, Supabase Auth, and Workbox for the service worker. The progression and nutrition engines live in a shared packages/engine directory as pure TypeScript with no I/O dependencies.
How it works
A user sets their goal, schedule, and available equipment during onboarding. MuscleBuddy generates a full training program — exercise selection, set and rep schemes, progression method, and deload schedule. Each week, the app tracks completed sets and logged weights to determine whether to advance load, hold, or trigger a deload. Weigh-ins feed a rolling average that drives automatic calorie adjustments toward the user's goal without requiring manual recalculation.
Coaches get a parallel interface: they can manage multiple clients, override any AI-generated recommendation, and configure their own methodology per client relationship. Client referrals earn coaches a 20–30% lifetime revenue share via Stripe Connect. The same PWA works installed on iOS and Android without going through an app store.