Mobile App Development for Personal Trainer
A personal trainer with 20+ clients loses hours to chat messages: "what exercise today?", "I forgot my program", "can we reschedule?". An app closes this channel and gives trainer a tool to sell online programs without physical presence.
Workout Plan — Most Non-trivial Part
Workout constructor is not just exercise list. Need flexible data structure:
Program → Week → Day → Workout → Exercise Set
├── sets: int
├── reps: String // "8-12" or "to failure"
├── weight: double?
├── rest: Duration
└── video_url: String?
Trainer creates program template, assigns to client, client sees their version. Load progression (add 2.5 kg next session) — either trainer manual adjustment or automatic per rule (if all sets completed with room — increase). Storage: drift (SQLite via Dart) for offline program access without internet in gym.
Rest timer between sets — critical for retention. Implementation via flutter_local_notifications with androidAllowWhileIdle: true — otherwise on Android 12+ timer won't work when phone in pocket.
HealthKit and Google Fit Integration
Clients want to see steps, heart rate, calories burned. iOS — HealthKit via health Flutter package. Android — Health Connect (new API, replaced Google Fit from 2023). Permission request must be contextual: not at app launch, but when user enters "progress" section. App Store rejects apps requesting HealthKit without clear purpose explanation.
Trainer Monetization
Two scenarios: B2C white-label (trainer pays subscription, gets branded app) or trainer marketplace. White-label simpler technically — one Flutter project, config via flavor and dart-define. Marketplace requires multi-tenancy, payment split (trainer 70%, platform 30%) via Stripe Connect.
Selling workout programs: if selling "digital content" via App Store — need In-App Purchase (Apple takes 30%). If client pays via website and just views in app — IAP not required. Important architectural decision at start.
Tech Stack and Key Components
Flutter + Riverpod + drift. Exercise videos — Cloudflare Stream or Vimeo Private (not YouTube because competitor ads). Trainer-client chat — Firebase Realtime Database. Progress analytics (weight graphs, load volume) — fl_chart package. Workout reminders — FCM + server scheduler (Laravel Scheduler or cron).
Timeline
MVP (programs, workout journal, chat, schedule): 9–13 weeks. With exercise video, HealthKit, program sales, analytics: 16–22 weeks. Cost calculated individually after analyzing monetization model.