[originalvichy]

Is that even possible with medial grade wrist devices? Apple Watches can perform it only during sleep which makes sense. It seems like a difficult problem to solve without a chest strap, or just measuring during sleep.

The only other alternative I can think of is a screen strap (some companies make those screenless ones, Polar, Whoop) around the bicep, as it’s relatively close to the shoulder and chest areas which gently move with our breath.

[roryirvine]

Garmin measures "photoplethysmography-derived respiration" (using the optical HR sensor). Error rates are under 1 breath per minute during sleep or at rest but rises during exercise, up to 4 bpm above the lactate threshold.

Impedance pneumography is more consistently accurate, but requires a chest (not bicep) strap.