Name: hrTSS
Rating: 3.8 (43 reviews)
Author: MattinG

hrTSS by default it works in trial mode and only runs for 30 minutes.

To activate the app to full mode contact me after donate 3,9€ attaching the email address - http://paypal.me/MattinG 

Supoort in https://forums.garmin.com/showthread.php?344188-hrTSS-DataField

Training Stress Score® (TSS) is a way of measuring how much stress is put on your body from a ride. To calculate TSS® is necesary a power meter or estimate with heart rate zones determinate by Joe Friel in this article: 

http://home.trainingpeaks.com/blog/article/estimating-training-stress-score-tss

To calculate hrTSS is necesary workout time series heart rate data and user threshold heart rate thas you can configure, with Garmin Express on your desktop or obile device (See the following link for more details https://apps.garmin.com/settingsHelp), If the threshold heart rate is not configured then it is estimated 85% of the theoretical maximum heart rate according to age.

Male Maximun Heart Rate = 220 – age
Female Maximun Heart Rate = 226 – age

You can see that it does not deviate much on the values offered by a potentiometer. : https://drive.google.com/open?id=1XEnR76PuxPgiAcSQIsEiaSlFvUEXdobi

Versions:
v5.3, v5.4, v5.5, v5.6, v5.7
- New device support
v5.2
- Persistant metric configurable. Activated consume more battery.
- Memory optimization.
v5.1 : 
+ Support for new devices
v5.0 : 
+ Persistent metric to not lose information in app/device resets.
+ Memory optimization for old devices.
v4.0 : 
+ Supoort for garmin new devices
+ Trial mode activated
v3.0:
+ Add a propertie to save the metrics values of activity and laps to FIT file
v2.2:
+ fixed crash when hr signal lost
v2.1:
+ fixed when heart rate erroneous reading crash the app now hrTSS is not calculated.
v2.0:
+ hrTSS not calculating when is stoped/paused
+ hrTSS value is recorded in datalfield until start the new ride
v1.0: 
+ Release