By default Fitness tracking (fitness step counter) is enabled on iPhone. Fitness tracking uses your body movements to determine your step count and fitness level.
Fitness tracking feature on iPhone aces as a pedometer and counts your steps in the background. Health and fitness apps on your iPhone ( including iPhone’s Health App ) use the Fitness tracking feature to determine your fitness activity.
1) Open the Settings app
2) On the Settings screen, scroll down & tap Privacy
3) Look for Motion & Fitness
4) Toggle on or off Fitness Tracking button
Note: Turning off Fitness Tracking will disable fitness tracking feature on all apps.