article in JAMA “Accuracy of Wrist-Worn Heart Rate Monitors”
"Wrist-Worn Heart Monitors Unreliable During Exercise Popular devices don't stand up to ECG" in http://www.medpagetoday.com/Cardiology/Prevention/60751?xid=nl_mpt_DHE_2016-10-13&eun=g848991d0r&pos=1 JAMA news: http://media.jamanetwork.com/news-item/study-finds-variable-accuracy-of-wrist-worn-heart-rate-monitors/