Complete Fitness App Development for Android

I'm seeking an experienced Android app developer to create a comprehensive fitness app from scratch. The app should include the following key features:

- Workout tracking
- Social sharing
- In-app purchases
- Physical activity tracking
- Fitness challenges

The app should also integrate with Google Fit, Strava, and Samsung Health. User authentication should be via email and password.

Ideal skills and experience:
- Proficiency in Android development
- Experience with fitness app features
- Familiarity with API integration for Google Fit, Strava, and Samsung Health
- Strong UI/UX design skills
- Knowledge of secure user authentication methods

Please provide examples of similar projects you've completed.