Functional and Non-Functional Requirements
Apple - Exercise
Practically requires a fitness tracker, can do some stuff without or with extra difficulty - Is all based around the Apple Fitness app which syncs with Apple Health 
Trends
Awards
History
You can also review individual workouts, finding info such as how long you worked out, average heart rate, total calories burned and more
You can also view more general information such as yearly data about different sports, i.e. - Running Distance - Cycling Distance - Swimming Distance - Downhill snow sports distance
Reminders
Help you keep track of your goals
Apple - Food and Nutrition
Has a nutrition section but it isn't very good, requires exact information to be inputted ( i.e. the milligrams of sodium in a drink )
Instead this section relies on third-party apps to provide information, such as: - MyFitnessPal - Ironically - Lifesum Which both massive food databases to allow for quick and easy entry of nutritional information
Apple health then displays this information with a breakdown of your macronutrients and micronutrients for the day, month and year
Apple - Weight Loss
Apples Health's weight loss section is pretty simplistic. Simply weigh yourself regularly and enter the data in, the app will compile this data and show you trends and changes over days, months or years
Can sync with smart scales
Apple - Body Composition
Similar to weight loss, Apple Health allows you to enter information such as height, body fat percentage, body mass index, lean body mass and waist circumference.
Again, these can be added manually but are intended to be used with smart scales and/or other fitness apps
Apple - Sleep
Allows you to enter information such as 'bed times' and when you plan to wake up, and then tracks your sleep between those times. Without a fitness tracker ( apple watch ) it does this by checking whether you've gone on your phone or iPad between those times With a tracker, it can measure morse useful information such as REM sleep Core sleep and Deep sleep times
Syncs from the Sleep App on Apple Watch or other third-party apps
Apple - Stress and Mindfulness
Little to no use without a third-party app ( For example, the Mindfulness app on apple watch )
The Mindfulness app gives you breathing instructions to help you relax and can give you reminders
Apple - Health Records
Allows you to import your health data from a doctor or clinic - Only two hospitals in the UK support this - More popular in America
Medical ID
Allows critical information to be accessed from the home screen ( on an iPhone ) such as medical conditions, allergies and blood type for paramedics to use. Can also show emergency contacts and even whether you are an organ donor
Apple - Export
Can export your data to a variety of services ( Email, Notes, Google Drive ) for sharing with health professionals.
Apple
MyFitnessPal - Exercise
Similar to Apple Health, MyFitnessPal requires syncing with a fitness tracker to show its full potential However, unlike Apple, MyFitnessPal does not have its own official fitness tracker like the Apple Watch. Instead it has partnered with many different companies to allow for easy integration
MyFitnessPal also allows you to record gym information such as reps and sets for different workouts, recording your improvements over time. If you don't have a fitness tracker, the app will use its algorithms to calculate how many calories you burned, and can show this relative to your calorie input
MyFitnessPal - Food and Nutrition
Can enter food details manually like Apple Health but mainly use either the search function, the barcode function or, if you have VIP, the AI function. Quick add feature that is also locked behind a pay wall
Has a big database of foods to directly import data without having to go through the hassle of copying all the nutrients down
MyFitnessPal - Weight Loss
Same as Apple, just a basic graph with trends and can sync with smart scales and other apps
MyFitnessPal - Body Composition
Tracks waist, neck and hips by default - though it is not easy to find Can add other measurements by have to go via the website?? Only body fat percent synced via third party apps ( like a smart scale )
MyFitnessPal - Sleep
Doesn't natively provide sleep tracking, requires Google's 'Health Connect' app
MyFitnessPal - Stress and Mindfulness
No support, native or third party
MyFitnessPal - Health Records
No support, native or third party
MyFitnessPal - Export
Can do a data export to a .csv file, however it requires premium