Yes, the Garmin’s first, second and third generation optical heart sensor hardware produces results with lower values than the Chest HRM.
Why is Optical Heart Rate generally lower:
1.) Wrist movement
2.) loose watch fit
3.) poor sensor contact
4.) hair, sweat or dirt will affect the values too
5.) Garmin Software filtering
Why are the high heart rate (Peaks) and low heart rate (valleys) missing:
Garmin Software imposes additional filters (Fast Fourier Transforms, FFT) in Activity types Strength Training, Tennis, Soccer and flexibility, due to high wrist movement in these activities. These FFT filters (advanced math) reduce the recorded peaks and valleys of a heart rate and calories calculations. Calories are based on heart rate, age, weight, gender and time.
There are a few solutions to improve the optical heart rate values:
1.) Wear the watch tighter. Poor sensor contact will result in lower HR values.
2.) Reduce wrist hair under sensor.
3.) Reduce wrist movement when possible, high movement reduces sensor contact.
4.) Chest HRM Gives best results.
Garmin Video explaining the difference between Optical and Chest Heart Rate monitors.
https://m.youtube.com/watch?v=LgQFD6GqlBs
