Running Heart Rate Straps vs. Optical Heart Rate Watches: Accuracy Differences and Best-Use Scenario Analysis

Introduction

Heart rate training is one of the foundations of modern endurance sports science. Whether it’s building an aerobic base with low-intensity Z2 long runs or stimulating cardiorespiratory fitness with Z4 lactate threshold training, the accuracy of heart rate data directly impacts training effectiveness. However, the question of “which method to use for measuring heart rate” confuses many runners: should they spend extra money on a chest strap heart rate monitor, or is relying on the optical heart rate sensor in their GPS watch sufficient?

How Heart Rate Straps (Chest Strap/Arm Strap) Work

Traditional chest strap heart rate monitors use electrocardiography (ECG) technology, sensing cardiac electrical signals through electrodes in contact with the skin to measure the R-R interval between two heartbeats (with millisecond-level precision).

Advantages:

• Highest accuracy, approaching medical-grade ECG precision
• Can measure heart rate variability (HRV) to assess recovery status
• Immediate response during high-intensity interval training (delay <1 second)
• Not affected by wrist movement

Disadvantages:

• Requires wearing an additional device, which can feel stuffy and uncomfortable, especially during Taiwan’s summer
• Requires periodic battery replacement or recharging
• In dry conditions, a small amount of water needs to be applied to the electrodes, otherwise the signal becomes unstable
• Representative brands: Garmin HRM-Pro Plus (approx. NT$3,500), Polar H10 (approx. NT$2,500)

How Optical Heart Rate (Watch-Mounted PPG Sensor) Works

Optical heart rate uses photoplethysmography (PPG), shining green LED light onto the skin to detect changes in blood flow within the blood vessels.

Advantages:

• No additional device needed, convenient to use
• Modern multi-wavelength sensors (green light + infrared) continue to improve in accuracy
• Comfortable to wear, suitable for all-day daily monitoring

Disadvantages:

• Wrist movement during high-intensity exercise causes motion artifacts, and heart rate readings may drift
• Darker skin pigmentation, tattoos, and straps that are too loose or too tight all affect accuracy
• Heart rate response has a delay of approximately 10–20 seconds, so it cannot reflect peak heart rate in real time during interval training

Accuracy Comparison Test Results

According to multiple independent reviews (DC Rainmaker, The Science of Sport, etc.):

Special Challenges of Summer Running in Taiwan

Taiwan’s summer heat and heavy sweating affect both heart rate measurement methods:

• Heart rate strap: Heavy sweat actually helps electrode contact, and the signal may become more stable
• Optical heart rate: Sweat can affect the strap’s position, causing the sensor to loosen; it is recommended to tighten the strap by one notch to ensure a secure fit

Additionally, a higher proportion of Taiwanese runners have darker skin tones, and some older optical heart rate sensors have lower light penetration for darker skin. It is recommended to prioritize newer watch models with multi-wavelength sensing technology.

Arm Strap Heart Rate Monitors: A Compromise Between the Two

The recently emerging arm strap optical heart rate monitors (such as the Polar Verity Sense and Garmin HRM-Fit) combine the independent measurement advantages of heart rate straps with the comfort of optical sensing. Blood vessels in the arm are less subject to movement interference than those in the wrist, and accuracy falls between chest strap heart rate monitors and wrist-worn optical heart rate sensors. They are a good choice for runners who want improved accuracy but don’t want to wear a chest strap (priced at approximately NT$2,000–3,500).

Practical Recommendations

• Beginners / fitness runners: Watch-mounted optical heart rate is sufficient; no need to purchase an additional heart rate strap
• Training-focused runners doing heart rate zone training: It is recommended to pair with a chest strap heart rate monitor, especially for interval training
• Ultramarathon runners / long-duration endurance events: Chest strap heart rate monitors offer better data stability
• Runners who want to measure HRV to optimize recovery management: A chest strap heart rate monitor is essential (Polar H10 is the top choice)

Conclusion

“The heart rate strap is more accurate” is an undisputed fact, but “optical heart rate is good enough” also holds true for most runners. The key is to understand your own training goals before deciding whether adding another piece of equipment is worth it. Regardless of which method you choose, the most important thing is to establish a consistent heart rate training habit, allowing the data to truly serve your running progress.

Related Reading

• Running Heart Rate Strap vs Optical Heart Rate: Choosing Between Accuracy and Use Cases
• Running Heart Rate Monitoring: In-Depth Accuracy Comparison Between Heart Rate Straps and Optical Heart Rate
• Heart Rate Strap vs Optical Heart Rate Watch: Which Is More Accurate for Running Training?
• Running Heart Rate Strap vs Optical Heart Rate: Measurement Accuracy and Wearing Comfort Comparison