Hi Urmas
1. Runtastic
Runtastic can access the built-in heart rate monitor on Apple Watch - as can other third-party apps, subject to the developers having taken advantage of that capability (which is available to them).
When using Runtastic, make sure that you start and stop the activity from the Runtastic app on your watch, not on your iPhone. Otherwise, the recorded heart rate information will not be saved.
If the app is not working as expected, check for and install any available update and also try restarting both devices (see question 2 below).
More information:
https://help.runtastic.com/hc/en-us/articles/204838802-Can-I-record-my-heart-rat e-with-Apple-Watch-
2. Activity + Exercise
In respect of inaccurate estimations for activity and exercise, it may help to reset your calibration data and start afresh:
- On your iPhone, in the Watch app, go to: My Watch (tab) > Privacy > Motion & Fitness > tap on Reset Calibration Data.
Activity estimations also depend on your personal information. To check that this has been entered accurately and to update it over time:
- On your iPhone, in the Watch app, go to: My Watch > Health > Edit (upper-right).
Check also that you are wearing Apple Watch snugly on the top of your wrist during workouts. To help with this, Apple suggests that you consider tightening your watch band before workouts and loosening it again afterwards.
It may also help to restart both your iPhone and your watch. Turn both devices off together, then restart your iPhone first:
- To turn your watch off: press and hold the side button until you see the Power Off slider; drag it to turn off;
- To turn it on: press and hold the side button until you see the Apple logo.
More information:
- Your heart rate. What it means, and where on Apple Watch you’ll find it. - Apple Support
- Use the Activity app on your Apple Watch - Apple Support
- Use the Workout app on your Apple Watch - Apple Support