Validity of Wearable Activity Monitors during Cycling and Resistance Exercise

Area of Science:

• Exercise Physiology
• Biomedical Engineering
• Wearable Technology

Background:

• Wearable activity monitors are increasingly popular for tracking exercise.
• The accuracy of heart rate (HR) and energy expenditure (EE) readings can be influenced by exercise type and intensity.
• Limited data exists on the validity of these devices during graded cycling and resistance exercises.

Purpose of the Study:

• To assess the validity of eight wearable activity monitors for HR measurement against an ECG.
• To evaluate the accuracy of seven wearable monitors for EE estimation compared to a metabolic analyzer.
• To compare monitor performance during both graded cycling and resistance exercise protocols.

Main Methods:

• Fifty participants (28 women, 22 men) underwent separate graded cycling and resistance exercise trials.
• Eight monitors (Apple Watch Series 2, Fitbit Blaze, Fitbit Charge 2, Polar H7, Polar A360, Garmin Vivosmart HR, TomTom Touch, Bose SoundSport Pulse) were tested.
• Heart rate was recorded post-intensity/set; energy expenditure was recorded post-protocol. Validity was defined as Mean Absolute Percent Error (MAPE) ≤10%.

Main Results:

• Polar H7 and Bose SoundSport Pulse (BSP) demonstrated valid HR readings during both cycling (MAPE 6.87%) and resistance exercise (MAPE 6.31%).
• Apple Watch Series 2 showed the highest HR validity during cycling (MAPE 4.14%), while BSP was most accurate during resistance exercise (MAPE 6.24%).
• HR underestimation increased with exercise intensity across devices; no monitor provided valid EE measurements for either exercise type.

Conclusions:

• Heart rate accuracy from wearable devices varies significantly with exercise intensity.
• Energy expenditure estimates from wearable devices are generally inaccurate.
• Users should exercise caution, as these devices are not medical-grade for monitoring physiological responses to exercise.