The purpose of this research is to compare four different heart rate monitors (Apple Watch Nike III,Fitbit Iconic, Garmin Vivosmart HR, Tom Tom Spark 3) to an Electrocardiograph (ECG) machine to determine the accuracy of the devices. Over the last two decades, there has been a proliferation of commercially available heart rate monitors. Elite athletes often use heart rate measurements to monitor training and fitness levels. In response, fitness companies have offered a variety of heart rate monitors to the general public. Previously, chest strap monitors that measured electrical activity were mainly used to track heart rates. More recently, wrist-worn monitors that use an optical sensor (light) to measure heart rate have gained in popularity. While the accuracy of chest strap monitors has been studied, there is currently no data concerning the accuracy of wrist-worn heart rate monitors. Assessment of the monitors' accuracy is important for subjects who rely upon the heart rate measurements to guide their athletic activity.

In 2018, worldwide sales of wearable fitness monitors are anticipated to exceed 110 million. Millions of consumers purchase fitness trackers that include heart rate monitors in order to help them to maintain their health and wellness. As popularity of these fitness devices grows, assessment and awareness of the accuracy of heart rate measurements becomes increasingly important.

In previous trials, the investigators assessed the accuracy of 4 wrist-worn HR monitors (Apple Watch, Fitbit Blaze, Garmin Forerunner 235, TomTom Spark Cardio) in healthy adult volunteers during various types of exercise. The investigators discovered that the accuracy varied with exercise type. With the treadmill, all devices were acceptable (rc =.88-.93) except the Fitbit Blaze (rc=.76). While biking, the Garmin and Apple Watch were acceptable (rc >.8). On the elliptical trainer without arm levers, only the Apple Watch provided accurate readings (rc=.94). None of the devices gave accurate readings for the elliptical trainer with arm levers (rc <.8). That study is now published.

Reviewers of the investigator's previous work raised an important question: how do commercial optical heart rate monitors perform when measuring heart rate in athletes performing at a high level of exertion? This study addresses that question.

The objective of this study is to evaluate the accuracy of four heart rate monitors in accomplished athletes (i.e. runners) performing at various levels of exertion, including a high level of exertion.

Inclusion Criteria:

• Age > 18 years
• Patients are able to run a mile in 7 minutes or less

Exclusion Criteria:

• Presence of a cardiac pacemaker
• Known chronic and persistent heart rhythm disorders
• Tattoos around the wrist or forearm area