Cross-Platform Athlete Monitoring App

I need a comprehensive athlete monitoring app developed for both iOS and Android platforms. The app should be able to track the following data:

- Physical Activity: Workouts and practice sessions
- Nutrition: Dietary intake
- Sleep Patterns: Sleep quality and duration
- Training Data: Specific metrics related to training sessions

Ideal skills and experience:
- Mobile app development for both iOS and Android
- Experience with health and fitness tracking applications
- Knowledge in data integration from various fitness APIs
- UI/UX design for a user-friendly interface
- Backend development to securely store and manage user data

Please provide examples of similar work done and your approach to ensure data accuracy and security.