HRV

I used welltory for a year, fairly accurate, now using Apple Watch. Super indicator on overall health.

Improvement plan: eat nutritious food, quit smoking, sleep well.

HRV is a great indicator of metabolic age

Not very familiar with it but there was an app named welltory (if I remember correctly) which used to take images (having flashlight on) of the blood flowing through your finger and then try to provide heart rate based on color variations.

Thanks, have read that breathing exercises also help.