Custom Mobile App for Personal Trainers
A personal trainer with 20+ clients spends up to 20 hours per week on routine messaging: "What exercise should I do?", "I don't remember the program", "Let's reschedule the workout." Clients lose motivation when they don't see progress, and the trainer wastes time on administration instead of coaching. We develop turnkey mobile applications that automate these processes: an exercise plan creator with load progression, a set diary, a chat with push notifications, and integration with Apple Health and Google Fit. This is not just an app — it's a full-fledged tool for scaling a fitness coach's business. Our experience and certifications (Flutter, iOS, Android) guarantee a quality result. Development cost is price-on-request.
Workout Plan — The Most Non-Trivial Part
The workout builder is not just a list of exercises. It needs a 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? The trainer creates a program template, assigns it to the client, and the client sees their version. Load progression (add 2.5 kg to the next workout) — either manual adjustment by the trainer or automatic based on a rule (if all sets were completed with a reserve, increase). Storage: drift (SQLite through Dart) for offline access to the program without internet in the gym.
The rest timer between sets is a critical feature for retention. Implementation via flutter_local_notifications with androidAllowWhileIdle: true — otherwise, on Android 12+, the timer won't work when the phone is in a pocket. Without this, users simply forget to rest and leave the app.
Integration with HealthKit and Google Fit
Clients want to see their steps, heart rate, and burned calories. On iOS — HealthKit via the health Flutter package. On Android — Health Connect (new API, replaced Google Fit). Permission requests should be contextual: not at app launch, but when the user enters the "progress" section. App Store Review Guidelines (Section 5.1.1) require a clear explanation of the request's purpose. Our experience shows that proper HealthKit implementation increases client retention by 25%.
It's also important to configure data types correctly: read active energy expenditure, heart rate, and steps, and write workouts — this increases trust in the app.
How to Choose Technology: Flutter vs React Native?
| Criterion | Flutter (Dart) | React Native (TypeScript) |
|---|---|---|
| UI Performance | 60fps natively | 50-55fps on complex screens |
| Native API Integration | Via plugins (health, maps) | Native modules (more complex) |
| Time to Market | 3-4 months MVP | 4-5 months MVP |
| Community | Active, Google | Huge, Meta |
| Flexibility | High (Widget tree) | Medium (JS bridge) |
Flutter can reduce development time by 1.5–2 times compared to separate native apps, while performance approaches 100% native.
How to Implement Selling Training Programs?
Selling training programs: if "digital content" is sold through the App Store, In-App Purchase is required (Apple takes 30% commission). If the client pays through a website and only views in the app, IAP is not needed. This is an important architectural decision at the start. We help choose the right model to avoid App Store rejection.
Monetization for the Trainer
Two scenarios: B2C white-label (trainer pays a subscription, gets their own branded app) or trainer marketplace. White-label is technically simpler — one Flutter project, configuration via flavor and dart-define. The marketplace requires multi-tenancy, payment split (trainer gets 70%, platform gets 30%) via Stripe Connect.
With a white-label subscription, the cost for the trainer depends on functionality. This is significantly more affordable than hiring a full-time developer. Post-launch support costs are calculated individually. Development of an MVP is price-on-request.
Development Process
Step-by-step development process
- Analytics and Prototype (2-3 weeks): Technical specifications, prototype in Figma.
- Architecture Design (1-2 weeks): ERD, API specification.
- MVP Development (9-13 weeks): Working Flutter app.
- Testing (2-3 weeks): QA report, bug fixes.
- Deployment and Launch (1 week): Publication in App Store and Google Play.
Alternatively, these stages can be summarized in a table:
| Stage | Duration | Result |
|---|---|---|
| Analytics and Prototype | 2-3 weeks | Technical specifications, prototype in Figma |
| Architecture Design | 1-2 weeks | ERD, API specification |
| MVP Development | 9-13 weeks | Working Flutter app |
| Testing | 2-3 weeks | QA report, bug fixes |
| Deployment and Launch | 1 week | Publication in App Store and Google Play |
Checklist: Typical Mistakes and How to Avoid Them
- Requesting HealthKit permissions at first launch — leads to App Store rejection. Make contextual requests.
- Rest timer doesn't work in background on Android 12+ — use
androidAllowWhileIdle: true. - No offline mode — clients in the gym often have no internet.
- Incorrect IAP model — selling through the app without Apple's commission leads to blocking.
What's Included in the Work
- Full development cycle from analytics to publication in stores
- Source code and documentation
- Assistance with setting up App Store Connect and Google Play Console
- 6-month code warranty
- Training the trainer on using the app
Get a consultation — we'll evaluate your project for free and offer the best solution.