Fenix 5 : advanced analytics/features that require an HR chest strap ?

Unless I've missed that discussion, surprisingly little (nothing ?) has been said about the requirement to use an HR chest strap instead of the optical HR sensor to get the new and advanced analytics offered on the F5.

Looking at https://buy.garmin.com/en-GB/GB/p/552237/pn/010-01685-13#overview it seems that the optical HR sensor will be able to deal with :
- Training Status
- Training Load
- Recovery Advisor (like on the FR235)

Chest strap required :
- Stress Score

TBD :
- Lactate Threshold Test : chest strap likely required as that's already the case on the FR735XT
- Functional Threshold Power : ?
- Training Effect 2.0 with aerobic and anaerobic benefit scores : ? but that would normally rely on HRV so needing a chest strap at this time
- Performance Condition : calculated after about 10' of running and then logged in the fit file/GC

Has anyone else been wondering about this ?

0 R_Tellis over 8 years ago

Yes, but the fact still remains that in order to measure HR, you need to measure beats over a time period. So if you can measure beats, you can measure the time between them, which is HRV. That's all I'm saying.

True enough however optical sensors are reading a difference in subcutaneous density created by a surge of blood flow through the capillaries instead of the electrical impulse that causes the heart to beat like a chest strap does. That surge of blood has travelled through probably meters worth arteries, veins, and capillaries by the time it gets to the skin under the sensor and won't have a definite peak to it which is what makes measuring the r-r interval in any precise way difficult, while the electrical impulse is a sharp and immediate spike.

It's like the difference between trying to detect the distance between peaks of waves on the ocean while sitting on the beach and measuring the distance between the points of the teeth of a saw. One is much more absolute while the other is a best guess.