Upgraded from Vivosmart 3 (wearing 24 a day) + Fenix 3 for trainings to New ! Fenix 5 + belt HRM Run for better accuracy
Ticket box to use previous device data set up a watch & start training! then:
1. Fenix 5 never detected my HR Max
2. Never detected my Lactate Treshold ( two times LT test failed , I was right in the zones but no results...)
3. I run , lift, row total 125 km 24 total trainings in 4 weeks Not at all automatic HR Max & LT detection!
4. Training Status & Load Showing completly different values comparing to Strava which I use for long time anf worked perfectly with my Fenix 3 !
Example Strava Weekly effort vs Garmin Load We can see between 12-18 August my Load went UP in strava ! Garmin Flat going down
5. HR zones ??? I left Fenix automaticly detect andf set zones based on my LT as I didi last few years with my fenix 3 worked perfectly with garmin connect & starva I had planty of good results cut a lt's of minutes on 10 km race!
Nothong work wit Fenix 5 !!!
Zones set automaticly by fenix 5 was completly wrong for that reason maybe my feeling about traing was not good and Load was missed out
Garmin auto 
Strava based on 181 HR MAX 
Garmin based on 181 HR MAx 
I changed my HR Zones today Setting Fenix on values from Strava, did workout 14 Km much better feeling regarding the HR Zones speed etc...
Looks like strava based on HR MAx & 20 € inscription a year do better job than fenix 5 a 500 € Having:
- avergare rest rate + 24 H HR
- automatic LT (in my case not detected)
- max HR (still not detected)