Name: Heart Rate Stress Score
Author: Rider68

This Datafield  calculates your training load based on your heart activity. The HRSS depends on exercise duration and intensity. The HRSS is based on an exponential scaling factor equation. 

The HRSS code is according to the web extension Elevate (former Name: Stravistix): http://thomaschampagne.github.io/elevate/
According to Stravistix, HRSS is more accurate than the Training Impulse TRIMP since it takes care of the user Lactate Threshold Heart Rate (LTHR). LTHR is the best average heart rate that an athlete can maintain for up to an hour. Training one hour at the LTHR results in an HRSS of 100.
HRSS is close to HrTSS® from TrainingPeaks™.


Calculation:
TRIMP= sum (D x HRR x 0.64 x e ^ (F x HRR) )  
HRSS = TRIMP x 100 / N

D is the duration in minutes at a particular Heart Rate
HRR is the Heart rate reserve of current HR
F is 1.92 for men and 1.67 for women
N is the 60 min HRSS at the LTHR.  N = 60 x HRR@LTHR x 0.64 x e ^ (F x HRR@LTHR)     
 
During your activity the device will display either HRSS, HRSS per hour, TRIMP or TRIMP per hour depending on your settings.
 
For calculation of the HRSS, the following user values have to be entered in the settings:

•	Resting heart rate (or alternatively the app can use Garmin's resting heart rate if available)
•	Maximum heart rate
•	Lactate Threshold Heart Rate (LTHR). 
If you don’t know your LTHR, a good approximation for LTHR is 85 - 90% of the maximum HR. 

These heart rate data can be changed with Garmin Express on your desktop or with you mobile device Connect App (See the following link for more details https://apps.garmin.com/settingsHelp).

In addition, your gender is taken from your Garmin user profile. Please check your user profile before using this datafield.

The HRSS information will be recorded to the FIT file and is visualized on the Garmin Connect platform. Two metrics (HRSS and HRSS per hour) are shown as graphs and as summary statistics.  


How to install the datafield on your device?
Please note that HRSS is being only calculated if the corresponding "data field" was added to one of the activity's data pages. A good explanation how to install a datafield on a garmin watch can be find here: https://tribeccato.com/2017/01/11/adding-data-fields-from-garmin-connect-iq/


Many thanks, when you consider the PayPal donation to my Connect IQ development here: http://www.paypal.me/ChristophK68