Are fitness watches bad for your health?

Are Fitness Watches Bad for Your Health?

Fitness watches are generally not harmful to health and may provide benefits for physical activity monitoring and heart rhythm detection, but they have limitations in accuracy that users should be aware of.

Benefits of Fitness Watches

• Fitness watches can help promote physical activity through self-monitoring, self-awareness, and self-determination, with studies showing that wearable device users report higher levels of walking, moderate physical activity, and total physical activity compared to non-users 1
• Wearable devices can inspire users' motivation and interest in physical activity through habit formation, potentially leading to decreased sedentary behavior 1
• Consumer wearables may provide similar measures for time in bed and time sleeping compared to research-grade accelerometers, making them potentially useful for sleep monitoring 2
• The American Heart Association recognizes the role of wearable activity monitors (WAMs) in healthcare settings for physical activity assessment and promotion 3

Accuracy Considerations

• EKG-based devices (like some Apple Watch models) are considered the gold standard for rhythm diagnosis with higher accuracy than PPG (photoplethysmography) based systems 4
• The Apple Watch Series 4 provides the highest validity when measuring heart rate during various physical activities, followed by Polar Vantage V, Garmin Fenix 5, and Fitbit Versa 5
• PPG technology (used in most fitness watches) is more susceptible to motion artifacts and may be affected by factors such as tattoos and darker skin tones 4, 3
• Fitness watches tend to be less accurate for measuring energy expenditure, with research showing none of the popular wrist-worn wearables should be employed to monitor energy expenditure at various intensities 5, 2

Potential Health Impacts

• Receiving accurate step counts from fitness watches can lead to improved mental health and aerobic capacity compared to no feedback, according to controlled studies 6
• However, exposure to artificially deflated step counts can lead to negative outcomes including more negative affect, reduced self-esteem and mental health, and increased blood pressure and heart rate 6
• Sleep quality has been reported to be significantly better among wearable device users compared to non-users 1

Limitations and Considerations

• The accuracy of heart rate measurements varies by activity type, with better accuracy during normal walking with torso placement, jogging with wrist placement, and slow walking with ankle placement 2
• Factors that can affect measurement accuracy include ambient temperature, skin characteristics, body height, and the type of activity being performed 3
• Fitness watches may overestimate time spent in higher-intensity activities and underestimate distance during faster-paced movement 2
• Consumer wearables have rapidly penetrated the health research space since 2014, but technical function, acceptability, and effectiveness must be validated in larger field studies 7

Medical Applications and Guidelines

• The FDA issued guidance for general wellness devices such as activity trackers and smartwatches in 2016, recognizing their role in improving physical fitness and wellness goals 3
• Professional medical societies have provided recommendations on the use of wearable devices for specific conditions like arrhythmia monitoring 3
• Smartwatches with ECG capability have shown promise in detecting atrial fibrillation with positive predictive values from 84% to 99% 4, 8
• The American Heart Association includes wearable activity monitors in their scientific statement on routine assessment and promotion of physical activity in healthcare settings 3

Conclusion

Fitness watches are not inherently bad for health and may provide benefits for physical activity monitoring and motivation. However, users should be aware of their limitations in accuracy, particularly for energy expenditure measurements. For medical applications, EKG-based devices provide higher accuracy than PPG-based systems, especially for heart rhythm detection.