[Research Review] Underwater Heart Rate Error Analysis: A Comparative Report of Optical Green Light Sensors vs. Chest Strap Heart Rate Monitors in Swimming: Exploring the Relationship Between Clinical Medicine and Athletic Performance (Article 1026)

Reference Journal Source: Journal of Sports Sciences • International Scientific Research Findings 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 by most sports watches) project green light LEDs onto the skin and detect changes in reflected light from blood flow to estimate heart rate. In swimming scenarios, there are three main sources of error:

• Water seepage interference: Water seeps through the gap between the strap and the skin, altering the contact between the sensor and the skin and disrupting the stability of the optical signal
• Repeated wrist muscle contraction: The stroking motion causes repeated compression of the wrist 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: When water temperature is low, peripheral blood vessels constrict, reducing blood flow to the superficial layers of the skin and weakening the optical signal intensity itself

Relative Advantages and Limitations of Chest Strap Heart Rate Monitors

Chest straps use electrodes to directly detect the heart’s electrical signals (similar to a simplified ECG) and are unaffected by changes in superficial skin blood flow. In theory, they offer higher accuracy and serve as the “gold standard” 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 loosening due to skin perspiration/water ingress, and some chest strap products have insufficient waterproof ratings to withstand extended water immersion.

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

Core Research Conclusions and Practical Recommendations

• Chest straps are the first choice for high-intensity training: If precise heart rate zone training is required (e.g., interval workouts), a chest strap heart rate monitor with sufficient waterproof rating is recommended
• Optical watches as a trend reference: Although optical sensing data contains errors, it can still serve as a reference for long-term training trends and overall intensity distribution; there is no need to completely abandon it due to errors
• 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 errors
• Combine with perceived exertion: When underwater heart rate data is unstable, the Rating of Perceived Exertion (RPE) scale can be used as a supplementary reference for pace adjustment

Common Research Q&A (FAQ)

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

A: This is mostly noise caused by optical signal interference from water flow and wrist muscle movement, rather than actual dramatic fluctuations in heart rate. It is recommended to interpret the data using trend lines rather than point values.

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

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

References and Academic Citations

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

Related Topic Reading

• 【Research Review】Underwater Heart Rate Error Analysis: A Comparative Report of Optical Green Light Sensors vs. Chest Strap Heart Rate Monitors in Swimming: Exploring the Relationship Between Clinical Medicine and Athletic Performance (Article 834)
• 【Research Review】Underwater Heart Rate Error Analysis: A Comparative Report of Optical Green Light Sensors vs. Chest Strap Heart Rate Monitors in Swimming: Exploring the Relationship Between Clinical Medicine and Athletic Performance (Article 792)
• 【Research Review】Underwater Heart Rate Error Analysis: A Comparative Report of Optical Green Light Sensors vs. Chest Strap Heart Rate Monitors in Swimming: Exploring the Relationship Between Clinical Medicine and Athletic Performance (Article 744)
• 【Research Review】Underwater Heart Rate Error Analysis: A Comparative Report of Optical Green Light Sensors vs. Chest Strap Heart Rate Monitors in Swimming: Exploring the Relationship Between Clinical Medicine and Athletic Performance (Article 228)