- Oct 25, 2014
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Do you have to wear the Band on the inside? It is very uncomfortable when sitting at my desk on the computer and I am scratching the heck out of it.
Yes, it will still work. What you describe is the watch being worn on the 'anterior aspect of the wrist', but the wording of the question really makes it sound like the face is turned 'inside out'.
The AW is actually not a true heart rate sensor (none of them are). They use heuristics to gauge the approximate rate at which the blood vessels dilate or contract. It is possible that the readings will be off from when the watch is worn on the posterior aspect of the wrist (the 'outside of the wrist') by a couple of beats increasing actual error rates. But those rates will be insignificant to most users. It is not intended as a medical device, but as a lifestyle device, so that's fine.
The field is called photoplethysmography (PPG). It basically uses an IR detector coupled with a photodetector.
The principle behind these sensors is optical detection of blood volume changes in the microvascular bed of the tissue. The sensor system consists of a light source and a detector, with red and infrared (IR) light-emitting diodes (LEDs) commonly used as the light source. The PPG sensor monitors changes in the light intensity via reflection from or transmission through the tissue. The changes in light intensity are associated with small variations in blood perfusion of the tissue and provide information on the cardiovascular system, in particular, the pulse rate. Due to the simplicity of this device, wearable PPG pulse rate sensors have been developed.Wearable Photoplethysmographic Sensors?Past and Present,
Toshiyo Tamura, Yuka Maeda, Masaki Sekine and Masaki Yoshida.
Electronics 2014, 3, 282-302; doi:10.3390/electronics3020282
As long as the tissue region has sufficient blood vessels/capillary networks, there will be sufficient signal present. The wrist region has two major pulsatile arteries (radial and ulnar) that will do the job for you. Both arteries are located closer to the palmar/anterior aspect than to the dorsal/outside of the wrist. They are fairly superficially located (EMTs can measure pulse at these locations). The anterior aspect is also glabrous (lacks hair) which presents a source of noise. So it is likely that wearing it on the inside might improve the signal quality. But the accuracy of the sensor in the end just depends on how the algorithms are designed - which aspect are they 'tuned' to. So there might be some error, but not significant.
Again, remember that this is not an accurate measurement device usable for cardiovascular diagnostics no matter what claims get made. The only true non-invasive cardiovascular measurements are provided by ultrasound (doppler sonography).
I find it works better on the outside. But is more usable on the inside. So flip it when doing exercise (outside) and rest of time. Could be my bony wrist though!
Either way is good.
I wear it on the outside exclusively. Makes it feel more like a watch to me and I don't have an issues seeing texts or emails.