Over the last two decades, there has been a proliferation of commercially available heart rate monitors. Recognizing that elite athletes often use heart rate to monitor training and assess aerobic fitness, fitness companies have offered a variety of heart rate monitoring systems to the general public. Recently, there has been a move from monitors that rely on chest straps to measure electrical activity toward more convenient, wrist-worn monitors that employ optical sensing technology similar to that used for pulse oximetry. While the accuracy of chest strap monitors has been assessed in a variety of studies, there is no data concerning the accuracy of wrist-worn heart rate monitors. Assessment of the monitors' accuracy is important both for the subjects who rely upon these monitors to guide their athletic activity and for the physicians to whom these individuals report their heart rate readings.

Physicians have long-used heart rate as an index of aerobic fitness and cardiovascular health. Resting heart rate has been linked to longevity and freedom from cardiovascular morbidity, and heart rate during exercise serves as a measure of aerobic capacity. In addition, heart rate recovery after exercise carries implications for an individuals' health.

Like physicians, coaches and athletic trainers employ heart rate measurement on a daily basis. In the athletic setting, heart rate during exercise is used as an indication of aerobic exertion. Elite athletes and their coaches often design workouts based upon achieved and targeted heart rates.

Once the province of physicians and elite athletes, heart rate monitoring has become widespread among the general public. In the nineteen eighties, fitness companies added heart rate monitors to their product lines. Systems employing a chest strap to monitor electrical activity, telemetry and a wrist-borne receiver became popular, and several controlled, scientific studies confirmed their accuracy.

More recently, manufacturers have marketed a new class of heart rate monitors that consist solely of wristwatch-style devices. These heart rate monitors use optical sensing technology to measure heart rate. While they offer convenience, their accuracy, particularly during exercise, is uncertain. A recent article in USA Today suggests that these wrist-worn monitors fail to provide accurate readings during exercise; however, to date there has been no rigorous scientific inquiry addressing this question.

The purpose of this study is to assess the accuracy of four popular, commercially available wrist-worn heart rate monitors under conditions of varying physical exertion.

Inclusion Criteria:

• Age > 18 years
• Able and willing to exercise (walk/jog) for a total of fifteen minutes

Exclusion Criteria:

• Health issues that preclude or contraindicate walking and/or jogging, including cardiovascular, orthopedic, pulmonary and other conditions
• Presence of a cardiac pacemaker
• Known cardiovascular disease
• Known heart rhythm disorders
• Use of Beta-blockers or antiarrhythmic medications
• Tattoos around the wrist area

Analysis was done per device. Each participant (50 total) wore 2 wrist devices in addition to a Polar H7 chest monitor and standard ECG monitor. Accuracy of the wrist devices was assessed using Concordance Correlation Coefficient.

1 day. Adverse events were collected during the active portion of the trial which constituted the time on the treadmill.