mobile app for fitness startup

I am looking for a mobile app developer to create a fitness app for my startup. The app should be developed for iOS platform and I have no preference for the programming language or framework. The main feature I am looking for is activity tracking.

Ideal skills and experience:
- Experience in iOS app development
- Proficiency in programming languages such as Swift or React Native
- Expertise in developing fitness or health apps
- Knowledge of activity tracking technology and integration with mobile apps