[Research Review] Underwater Heart Rate Error Analysis: Comparison of Optical Green Light Sensors and Chest Strap Heart Rate Monitors in Swimming — Report: Exploring the Relationship Between Clinical Medicine and Sports Performance (Article 204)

Reference Journal Source: Journal of Sports Sciences • International Scientific Research Review Series

This article explores the sources of error in underwater heart rate measurement, comparing the accuracy differences between optical green light sensors (PPG) and chest strap heart rate monitors (ECG-based) in swimming environments.

Sources of Error in Optical Heart Rate Sensing

Optical heart rate sensors (used in most sports watches) estimate heart rate by shining green LED light onto the skin and detecting changes in light reflected from blood flow. In swimming scenarios, there are three main sources of error:

• Water seepage interference: Water seeps through the gap between the strap and skin, altering the contact between the sensor and skin, and disrupting the stability of the optical signal
• Repeated forearm muscle contraction: The swimming stroke causes repeated compression of the forearm muscles and subcutaneous tissue, making the optical signal susceptible to contamination from muscle blood flow signals, which are difficult to distinguish from heartbeat signals
• Cold-induced vasoconstriction: In colder water, peripheral blood vessels constrict, reducing blood flow to the superficial layers of the skin, which weakens the optical signal intensity itself

Relative Advantages and Limitations of Chest Strap Heart Rate Monitors

Chest straps directly detect the heart’s electrical signals via electrodes (similar to a simplified ECG) and are unaffected by changes in superficial skin blood flow, theoretically offering higher accuracy and serving as the “gold standard” comparison reference used in most sports science research. However, chest straps still have limitations in swimming scenarios: they require good contact to maintain signal stability, prolonged swimming may cause electrode contact to loosen due to skin sweating/water ingress, and some chest strap products have insufficient waterproof ratings to withstand prolonged submersion.

Comparison of Error Magnitudes Between the Two Sensing Methods (Illustrative)

Core Research Conclusions and Practical Recommendations

• Choose chest straps for high-intensity training: If precise heart rate zone training is needed (e.g., interval workouts), it is recommended to use a chest strap heart rate monitor with sufficient waterproof rating
• Optical watches as trend reference: Although optical sensing data contains errors, it can still serve as a reference for long-term training trends and approximate intensity distribution; there is no need to abandon it entirely due to error
• Verify device fit: Regardless of the sensing method, confirming that the device fits snugly but comfortably before training is the most direct and effective way to reduce error
• Combine with perceived exertion: When underwater heart rate data is unstable, the Rating of Perceived Exertion (RPE) scale can be used as a supplementary aid for pace adjustment

Common Research Q&A (FAQ)

Q: Why does the watch heart rate often fluctuate erratically during swimming?

A: This is mostly noise caused by optical signals being interfered with by water flow and wrist muscle movement, rather than actual dramatic fluctuations in heart rate. It is recommended to interpret data using trend lines rather than single-point values.

Q: Are all chest strap heart rate monitors suitable for swimming?

A: No. You need to confirm that the product explicitly indicates a waterproof rating suitable for water use and the signal transmission method (some chest straps using Bluetooth transmission will lose signal underwater; models with underwater memory storage functionality should be selected).

References and Academic Citations

1. Journal of Sports Sciences — Research direction related to accuracy comparison of wearable device heart rate measurement.
2. IEEE Journal of Biomedical and Health Informatics — Literature related to signal noise processing in optical heart rate sensing.

Further Reading

• Research Review: Underwater Heart Rate Error Analysis: Comparison of Optical Green Light Sensors and Chest Strap Heart Rate Monitors in Swimming — Report: Exploring the Relationship Between Clinical Medicine and Sports Performance (Article 624)
• Research Review: Underwater Heart Rate Error Analysis: Comparison of Optical Green Light Sensors and Chest Strap Heart Rate Monitors in Swimming — Report: Exploring the Relationship Between Clinical Medicine and Sports Performance (Article 741)
• Research Review: Underwater Heart Rate Error Analysis: Comparison of Optical Green Light Sensors and Chest Strap Heart Rate Monitors in Swimming — Frontiers in Exercise Physiology Research Progress (Article 1128)
• Research Review: Underwater Heart Rate Error Analysis: Comparison of Optical Green Light Sensors and Chest Strap Heart Rate Monitors in Swimming — Frontiers in Exercise Physiology Research Progress (Article 675)