Does a polar chest strap pair with an Apple Watch more accurately than an Apple Watch alone on low, moderate, and high exercise intensities? A cross-sectional study.

Background: The Apple Watch measures heart rate, but its validity decreases with high exercise intensities, so this study investigated whether pairing the Apple Watch with a polar chest strap could be more accurate than the Apple Watch alone in measuring heart rate during high intensity exercises and in recovery from exercises.

Methods: A cross-sectional study measured heart rate on the Apple Watch compared to the Apple Watch paired with the Polar chest strap on 30 healthy subjects. Each participant has done three minutes of low, moderate, and high exercise intensities using both the treadmill and cycle for 9 minutes each, followed by 3 minutes of recovery after each treadmill and cycle.

Results: There were excellent correlations between the Apple Watch and Polar chest strap during low (r=0.99 Treadmill, r=0.99 cycle), moderate (r=0.99 treadmill, r=0.99 cycle), and high (r=0.96 treadmill, r=0.99 cycle), exercise intensities and in recovery from Treadmill and Cycle (r=0.97 treadmill, r=0.98 cycle). There were excellent correlations between the combined Apple Watch with Polar chest strap and the Apple Watch alone during low (r=1.00 treadmill, r=0.99 cycle), moderate (r=0.99 treadmill, r=0.99 cycle), and high (r=0.99 treadmill, r=0.99 cycle) exercise intensities and in recovery from Treadmill and Cycle (r=1.00 treadmill, r=0.99 cycle).

Conclusions: The Apple Watch is valid for measuring heart rate during low to moderate exercise intensity, and its validity can be increased at high exercise intensities or after recovery from exercise by adding it to the Polar chest strap and holding hands on the handrail while performing exercises.